py3: add Python 3 output for test-flagprocessor.t

The exception is being generated from ui.traceback(), which
simply calls traceback.format_*() to format exceptions. Since
the output from the standard library has changed, there is
seemingly not much we can do about it. So this commit adds
conditional output depending on the Python version.

I'm not thrilled about b'' appearing in user-facing output.
Can we do something better here?

Differential Revision: https://phab.mercurial-scm.org/D5806

tests/test-flagprocessor.t

@@ -1,302 +1,304 b''
 # Create server
   $ hg init server
   $ cd server
   $ cat >> .hg/hgrc << EOF
   > [extensions]
   > extension=$TESTDIR/flagprocessorext.py
   > EOF
   $ cd ../
 
 # Clone server and enable extensions
   $ hg clone -q server client
   $ cd client
   $ cat >> .hg/hgrc << EOF
   > [extensions]
   > extension=$TESTDIR/flagprocessorext.py
   > EOF
 
 # Commit file that will trigger the noop extension
   $ echo '[NOOP]' > noop
   $ hg commit -Aqm "noop"
 
 # Commit file that will trigger the base64 extension
   $ echo '[BASE64]' > base64
   $ hg commit -Aqm 'base64'
 
 # Commit file that will trigger the gzip extension
   $ echo '[GZIP]' > gzip
   $ hg commit -Aqm 'gzip'
 
 # Commit file that will trigger noop and base64
   $ echo '[NOOP][BASE64]' > noop-base64
   $ hg commit -Aqm 'noop+base64'
 
 # Commit file that will trigger noop and gzip
   $ echo '[NOOP][GZIP]' > noop-gzip
   $ hg commit -Aqm 'noop+gzip'
 
 # Commit file that will trigger base64 and gzip
   $ echo '[BASE64][GZIP]' > base64-gzip
   $ hg commit -Aqm 'base64+gzip'
 
 # Commit file that will trigger base64, gzip and noop
   $ echo '[BASE64][GZIP][NOOP]' > base64-gzip-noop
   $ hg commit -Aqm 'base64+gzip+noop'
 
 # TEST: ensure the revision data is consistent
   $ hg cat noop
   [NOOP]
   $ hg debugdata noop 0
   [NOOP]
 
   $ hg cat -r . base64
   [BASE64]
   $ hg debugdata base64 0
   W0JBU0U2NF0K (no-eol)
 
   $ hg cat -r . gzip
   [GZIP]
   $ hg debugdata gzip 0
   x\x9c\x8bv\x8f\xf2\x0c\x88\xe5\x02\x00\x08\xc8\x01\xfd (no-eol) (esc)
 
   $ hg cat -r . noop-base64
   [NOOP][BASE64]
   $ hg debugdata noop-base64 0
   W05PT1BdW0JBU0U2NF0K (no-eol)
 
   $ hg cat -r . noop-gzip
   [NOOP][GZIP]
   $ hg debugdata noop-gzip 0
   x\x9c\x8b\xf6\xf3\xf7\x0f\x88\x8dv\x8f\xf2\x0c\x88\xe5\x02\x00\x1dH\x03\xf1 (no-eol) (esc)
 
   $ hg cat -r . base64-gzip
   [BASE64][GZIP]
   $ hg debugdata base64-gzip 0
   eJyLdnIMdjUziY12j/IMiOUCACLBBDo= (no-eol)
 
   $ hg cat -r . base64-gzip-noop
   [BASE64][GZIP][NOOP]
   $ hg debugdata base64-gzip-noop 0
   eJyLdnIMdjUziY12j/IMiI328/cPiOUCAESjBi4= (no-eol)
 
 # Push to the server
   $ hg push
   pushing to $TESTTMP/server
   searching for changes
   adding changesets
   adding manifests
   adding file changes
   added 7 changesets with 7 changes to 7 files
 
 Ensure the data got to the server OK
 
   $ cd ../server
   $ hg cat -r 6e48f4215d24 noop
   [NOOP]
   $ hg debugdata noop 0
   [NOOP]
 
   $ hg cat -r 6e48f4215d24 base64
   [BASE64]
   $ hg debugdata base64 0
   W0JBU0U2NF0K (no-eol)
 
   $ hg cat -r 6e48f4215d24 gzip
   [GZIP]
   $ hg debugdata gzip 0
   x\x9c\x8bv\x8f\xf2\x0c\x88\xe5\x02\x00\x08\xc8\x01\xfd (no-eol) (esc)
 
   $ hg cat -r 6e48f4215d24 noop-base64
   [NOOP][BASE64]
   $ hg debugdata noop-base64 0
   W05PT1BdW0JBU0U2NF0K (no-eol)
 
   $ hg cat -r 6e48f4215d24 noop-gzip
   [NOOP][GZIP]
   $ hg debugdata noop-gzip 0
   x\x9c\x8b\xf6\xf3\xf7\x0f\x88\x8dv\x8f\xf2\x0c\x88\xe5\x02\x00\x1dH\x03\xf1 (no-eol) (esc)
 
   $ hg cat -r 6e48f4215d24 base64-gzip
   [BASE64][GZIP]
   $ hg debugdata base64-gzip 0
   eJyLdnIMdjUziY12j/IMiOUCACLBBDo= (no-eol)
 
   $ hg cat -r 6e48f4215d24 base64-gzip-noop
   [BASE64][GZIP][NOOP]
   $ hg debugdata base64-gzip-noop 0
   eJyLdnIMdjUziY12j/IMiI328/cPiOUCAESjBi4= (no-eol)
 
 # Initialize new client (not cloning) and setup extension
   $ cd ..
   $ hg init client2
   $ cd client2
   $ cat >> .hg/hgrc << EOF
   > [paths]
   > default = $TESTTMP/server
   > [extensions]
   > extension=$TESTDIR/flagprocessorext.py
   > EOF
 
 # Pull from server and update to latest revision
   $ hg pull default
   pulling from $TESTTMP/server
   requesting all changes
   adding changesets
   adding manifests
   adding file changes
   added 7 changesets with 7 changes to 7 files
   new changesets 07b1b9442c5b:6e48f4215d24
   (run 'hg update' to get a working copy)
   $ hg update
   7 files updated, 0 files merged, 0 files removed, 0 files unresolved
 
 # TEST: ensure the revision data is consistent
   $ hg cat noop
   [NOOP]
   $ hg debugdata noop 0
   [NOOP]
 
   $ hg cat -r . base64
   [BASE64]
   $ hg debugdata base64 0
   W0JBU0U2NF0K (no-eol)
 
   $ hg cat -r . gzip
   [GZIP]
   $ hg debugdata gzip 0
   x\x9c\x8bv\x8f\xf2\x0c\x88\xe5\x02\x00\x08\xc8\x01\xfd (no-eol) (esc)
 
   $ hg cat -r . noop-base64
   [NOOP][BASE64]
   $ hg debugdata noop-base64 0
   W05PT1BdW0JBU0U2NF0K (no-eol)
 
   $ hg cat -r . noop-gzip
   [NOOP][GZIP]
   $ hg debugdata noop-gzip 0
   x\x9c\x8b\xf6\xf3\xf7\x0f\x88\x8dv\x8f\xf2\x0c\x88\xe5\x02\x00\x1dH\x03\xf1 (no-eol) (esc)
 
   $ hg cat -r . base64-gzip
   [BASE64][GZIP]
   $ hg debugdata base64-gzip 0
   eJyLdnIMdjUziY12j/IMiOUCACLBBDo= (no-eol)
 
   $ hg cat -r . base64-gzip-noop
   [BASE64][GZIP][NOOP]
   $ hg debugdata base64-gzip-noop 0
   eJyLdnIMdjUziY12j/IMiI328/cPiOUCAESjBi4= (no-eol)
 
 # TEST: ensure a missing processor is handled
   $ echo '[FAIL][BASE64][GZIP][NOOP]' > fail-base64-gzip-noop
   $ hg commit -Aqm 'fail+base64+gzip+noop'
   abort: missing processor for flag '0x1'!
   [255]
   $ rm fail-base64-gzip-noop
 
 # TEST: ensure we cannot register several flag processors on the same flag
   $ cat >> .hg/hgrc << EOF
   > [extensions]
   > extension=$TESTDIR/flagprocessorext.py
   > duplicate=$TESTDIR/flagprocessorext.py
   > EOF
   $ hg debugrebuilddirstate
   Traceback (most recent call last):
     File "*/mercurial/extensions.py", line *, in _runextsetup (glob)
       extsetup(ui)
     File "*/tests/flagprocessorext.py", line *, in extsetup (glob)
       validatehash,
     File "*/mercurial/revlog.py", line *, in addflagprocessor (glob)
       _insertflagprocessor(flag, processor, _flagprocessors)
     File "*/mercurial/revlog.py", line *, in _insertflagprocessor (glob)
       raise error.Abort(msg)
-  Abort: cannot register multiple processors on flag '0x8'.
+  mercurial.error.Abort: b"cannot register multiple processors on flag '0x8'." (py3 !)
+  Abort: cannot register multiple processors on flag '0x8'. (no-py3 !)
   *** failed to set up extension duplicate: cannot register multiple processors on flag '0x8'.
   $ hg st 2>&1 | egrep 'cannot register multiple processors|flagprocessorext'
     File "*/tests/flagprocessorext.py", line *, in extsetup (glob)
-  Abort: cannot register multiple processors on flag '0x8'.
+  mercurial.error.Abort: b"cannot register multiple processors on flag '0x8'." (py3 !)
+  Abort: cannot register multiple processors on flag '0x8'. (no-py3 !)
   *** failed to set up extension duplicate: cannot register multiple processors on flag '0x8'.
     File "*/tests/flagprocessorext.py", line *, in b64decode (glob)
 
   $ cd ..
 
 # TEST: bundle repo
   $ hg init bundletest
   $ cd bundletest
 
   $ cat >> .hg/hgrc << EOF
   > [extensions]
   > flagprocessor=$TESTDIR/flagprocessorext.py
   > EOF
 
   $ for i in 0 single two three 4; do
   >   echo '[BASE64]a-bit-longer-'$i > base64
   >   hg commit -m base64-$i -A base64
   > done
 
   $ hg update 2 -q
   $ echo '[BASE64]a-bit-longer-branching' > base64
   $ hg commit -q -m branching
 
 #if repobundlerepo
   $ hg bundle --base 1 bundle.hg
   4 changesets found
   $ hg --config extensions.strip= strip -r 2 --no-backup --force -q
   $ hg -R bundle.hg log --stat -T '{rev} {desc}\n' base64
   5 branching
    base64 |  2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)
   
   4 base64-4
    base64 |  2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)
   
   3 base64-three
    base64 |  2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)
   
   2 base64-two
    base64 |  2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)
   
   1 base64-single
    base64 |  2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)
   
   0 base64-0
    base64 |  1 +
    1 files changed, 1 insertions(+), 0 deletions(-)
   
 
   $ hg bundle -R bundle.hg --base 1 bundle-again.hg -q
   $ hg -R bundle-again.hg log --stat -T '{rev} {desc}\n' base64
   5 branching
    base64 |  2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)
   
   4 base64-4
    base64 |  2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)
   
   3 base64-three
    base64 |  2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)
   
   2 base64-two
    base64 |  2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)
   
   1 base64-single
    base64 |  2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)
   
   0 base64-0
    base64 |  1 +
    1 files changed, 1 insertions(+), 0 deletions(-)
   
   $ rm bundle.hg bundle-again.hg
 #endif
 
 # TEST: hg status
 
   $ hg status
   $ hg diff