py3: add b'' prefixes in tests/test-custom-filters.t

# skip-blame because just b'' prefixes

Differential Revision: https://phab.mercurial-scm.org/D3595

tests/test-custom-filters.t

@@ -1,66 +1,66 b''
   $ hg init
 
   $ cat > .hg/hgrc <<EOF
   > [extensions]
   > prefixfilter = prefix.py
   > [encode]
   > *.txt = stripprefix: Copyright 2046, The Masters
   > [decode]
   > *.txt = insertprefix: Copyright 2046, The Masters
   > EOF
 
   $ cat > prefix.py <<EOF
   > from mercurial import error
   > def stripprefix(s, cmd, filename, **kwargs):
-  >     header = '%s\n' % cmd
+  >     header = b'%s\n' % cmd
   >     if s[:len(header)] != header:
-  >         raise error.Abort('missing header "%s" in %s' % (cmd, filename))
+  >         raise error.Abort(b'missing header "%s" in %s' % (cmd, filename))
   >     return s[len(header):]
   > def insertprefix(s, cmd):
-  >     return '%s\n%s' % (cmd, s)
+  >     return b'%s\n%s' % (cmd, s)
   > def reposetup(ui, repo):
-  >     repo.adddatafilter('stripprefix:', stripprefix)
-  >     repo.adddatafilter('insertprefix:', insertprefix)
+  >     repo.adddatafilter(b'stripprefix:', stripprefix)
+  >     repo.adddatafilter(b'insertprefix:', insertprefix)
   > EOF
 
   $ cat > .hgignore <<EOF
   > .hgignore
   > prefix.py
   > prefix.pyc
   > EOF
 
   $ cat > stuff.txt <<EOF
   > Copyright 2046, The Masters
   > Some stuff to ponder very carefully.
   > EOF
   $ hg add stuff.txt
   $ hg ci -m stuff
 
 Repository data:
 
   $ hg cat stuff.txt
   Some stuff to ponder very carefully.
 
 Fresh checkout:
 
   $ rm stuff.txt
   $ hg up -C
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   $ cat stuff.txt
   Copyright 2046, The Masters
   Some stuff to ponder very carefully.
   $ echo "Very very carefully." >> stuff.txt
   $ hg stat
   M stuff.txt
 
   $ echo "Unauthorized material subject to destruction." > morestuff.txt
 
 Problem encoding:
 
   $ hg add morestuff.txt
   $ hg ci -m morestuff
   abort: missing header "Copyright 2046, The Masters" in morestuff.txt
   [255]
   $ hg stat
   M stuff.txt
   A morestuff.txt