obsfate: fix changeset description diff computing
Mercurial core 8b6dd3922f70 changed the mdiff.unidiff API. Add a new compat
method for all supported Mercurial versions.
# utility to setup pythonpath to point into the tested repository
export SRCDIR=`dirname $TESTDIR`
if [ -n "$PYTHONPATH" ]; then
export HGTEST_ORIG_PYTHONPATH=$PYTHONPATH
export PYTHONPATH=$SRCDIR:$PYTHONPATH
else
export PYTHONPATH=$SRCDIR
fi