Emacs: follow the revision usage policy of "hg diff" command.
This patche makes "parent" as default revision of diff command.
to build a new macosx binary package:
install macpython from http://undefined.org/python/
install py2app from http://pythonmac.org/packages/
make sure /usr/local/bin is in your path
run bdist_mpkg in top-level hg directory
find packaged stuff in dist directory