setup: fixed for Pythons which don't have a CFLAGS
Specifically this is observed to happen on the PyPy one gets from homebrew
to build a new macosx binary package:
install macpython from http://www.python.org/download/mac
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