blackbox: don't run permission tests on non-unix systems

The windows and vfat test runs were failing due to read/write permissions not
working the same on those systems.  On vfat, permissions can't be changed
at all, and on windows it seems the chmod emulation doesn't remove read
permissions.  We could theoretically get the 'cannot write to blacklog.log'
test to pass on windows but there's no #if condition to let us exclude vfat
only.

Verified that test-blackbox passes on windows now.

tests/test-blackbox.t

@@ -1,150 +1,154 b''
 setup
   $ cat > mock.py <<EOF
   > from mercurial import util
   > 
   > def makedate():
   >     return 0, 0
   > def getuser():
   >     return 'bob'
   > # mock the date and user apis so the output is always the same
   > def uisetup(ui):
   >     util.makedate = makedate
   >     util.getuser = getuser
   > EOF
   $ cat >> $HGRCPATH <<EOF
   > [extensions]
   > blackbox=
   > mock=`pwd`/mock.py
   > mq=
   > EOF
   $ hg init blackboxtest
   $ cd blackboxtest
 
 command, exit codes, and duration
 
   $ echo a > a
   $ hg add a
   $ hg blackbox
   1970/01/01 00:00:00 bob> add a
   1970/01/01 00:00:00 bob> add exited 0 after * seconds (glob)
 
 incoming change tracking
 
 create two heads to verify that we only see one change in the log later
   $ hg commit -ma
   $ hg up null
   0 files updated, 0 files merged, 1 files removed, 0 files unresolved
   $ echo b > b
   $ hg commit -Amb
   adding b
   created new head
 
 clone, commit, pull
   $ hg clone . ../blackboxtest2
   updating to branch default
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   $ echo c > c
   $ hg commit -Amc
   adding c
   $ cd ../blackboxtest2
   $ hg pull
   pulling from $TESTTMP/blackboxtest (glob)
   searching for changes
   adding changesets
   adding manifests
   adding file changes
   added 1 changesets with 1 changes to 1 files
   (run 'hg update' to get a working copy)
   $ hg blackbox -l 3
   1970/01/01 00:00:00 bob> pull
   1970/01/01 00:00:00 bob> 1 incoming changes - new heads: d02f48003e62
   1970/01/01 00:00:00 bob> pull exited None after * seconds (glob)
 
 we must not cause a failure if we cannot write to the log
 
   $ hg rollback
   repository tip rolled back to revision 1 (undo pull)
+
+#if unix-permissions
   $ chmod 000 .hg/blackbox.log
   $ hg --debug incoming
   warning: cannot write to blackbox.log: Permission denied
   comparing with $TESTTMP/blackboxtest (glob)
   query 1; heads
   searching for changes
   all local heads known remotely
   changeset:   2:d02f48003e62c24e2659d97d30f2a83abe5d5d51
   tag:         tip
   phase:       draft
   parent:      1:6563da9dcf87b1949716e38ff3e3dfaa3198eb06
   parent:      -1:0000000000000000000000000000000000000000
   manifest:    2:ab9d46b053ebf45b7996f2922b9893ff4b63d892
   user:        test
   date:        Thu Jan 01 00:00:00 1970 +0000
   files+:      c
   extra:       branch=default
   description:
   c
   
   
+#endif
   $ hg pull
   pulling from $TESTTMP/blackboxtest (glob)
   searching for changes
   adding changesets
   adding manifests
   adding file changes
   added 1 changesets with 1 changes to 1 files
   (run 'hg update' to get a working copy)
 
 a failure reading from the log is fine
-
+#if unix-permissions
   $ hg blackbox -l 3
   abort: Permission denied: $TESTTMP/blackboxtest2/.hg/blackbox.log
   [255]
 
   $ chmod 600 .hg/blackbox.log
+#endif
 
 backup bundles get logged
 
   $ touch d
   $ hg commit -Amd
   adding d
   created new head
   $ hg strip tip
   0 files updated, 0 files merged, 1 files removed, 0 files unresolved
   saved backup bundle to $TESTTMP/blackboxtest2/.hg/strip-backup/*-backup.hg (glob)
   $ hg blackbox -l 3
   1970/01/01 00:00:00 bob> strip tip
   1970/01/01 00:00:00 bob> saved backup bundle to $TESTTMP/blackboxtest2/.hg/strip-backup/*-backup.hg (glob)
   1970/01/01 00:00:00 bob> strip exited 0 after * seconds (glob)
 
 extension and python hooks - use the eol extension for a pythonhook
 
   $ echo '[extensions]' >> .hg/hgrc
   $ echo 'eol=' >> .hg/hgrc
   $ echo '[hooks]' >> .hg/hgrc
   $ echo 'update = echo hooked' >> .hg/hgrc
   $ hg update
   hooked
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
   $ hg blackbox -l 4
   1970/01/01 00:00:00 bob> update
   1970/01/01 00:00:00 bob> pythonhook-preupdate: hgext.eol.preupdate finished in * seconds (glob)
   1970/01/01 00:00:00 bob> exthook-update: echo hooked finished in * seconds (glob)
   1970/01/01 00:00:00 bob> update exited False after * seconds (glob)
 
 log rotation
 
   $ echo '[blackbox]' >> .hg/hgrc
   $ echo 'maxsize = 20 b' >> .hg/hgrc
   $ echo 'maxfiles = 3' >> .hg/hgrc
   $ hg status
   $ hg status
   $ hg status
   $ hg tip -q
   2:d02f48003e62
   $ ls .hg/blackbox.log*
   .hg/blackbox.log
   .hg/blackbox.log.1
   .hg/blackbox.log.2
 
 cleanup
   $ cd ..