Makefile: Fix PACKAGE_VERSION extraction

Makefile: Fix PACKAGE_VERSION extraction

The old method grepped for __version__ in catalyst.  That broke with
24c5352 (Initial rearrangement of the python directories, 2013-01-10),
which moved catalyst to bin/catalyst, kept the __version__ in
bin/catalyst, and added a new __version__ in catalyst/main.py.  Then
46b261e (setup.py: Add disutils-based packaging, 2013-06-05)
consolidated the __version__ definitions in catalyst/__init__.py,
removing them from bin/catalyst and catalyst/main.py.  This patch
adjusts the Makefile, invoking Python to extract catalyst.__version__
instead of grepping through the file that defines it.