This checkin adds a symlink to the lib directory of a framework install

This checkin adds a symlink to the lib directory of a framework install
of Python (on OSX), and the end result of that is that the combination of
``python-config --ldflags`` and ``python-config --libs`` refers to an actually
existing location.

I've done this in preference to changing python-config to specify
'-framework Python' for linking because that doesn't work when you have multiple
versions of python installed (because '-framework Python' will always link to
the 'Current' version of the framework, without a possibility to specify a
specific version).