convert: use encoding.encoding instead of locale.getpreferredencoding()
The latter may not return useful results in certain OS X environments.
#!/bin/sh
hg init a
cd a
cp $TESTDIR/binfile.bin .
hg add binfile.bin
hg ci -m 'add binfile.bin'
echo >> binfile.bin
hg ci -m 'change binfile.bin'
hg revert -r 0 binfile.bin
hg ci -m 'revert binfile.bin'
echo % diff -r 0 -r 1
hg diff --nodates -r 0 -r 1
echo % diff -r 0 -r 2
hg diff --nodates -r 0 -r 2
echo % diff --git -r 0 -r 1
hg diff --git -r 0 -r 1
echo % diff --git -r 0 -r 2
hg diff --git -r 0 -r 2