build the python interface

build the python interface
CMake can build the python version (and on os x/unix test it)
CMakes targets aren't quite appropriate for python extensions the
ADD_LIBRARY target gets the right build settings but names the file
libX.so while python needs X.so. I got around this by adding a custom
command which makes a symlink to the right name--of course that depends
on shell commands not available on windows. :(

Also there's some problems with boost.python not knowing about the
string to boost/filesystem converter. I manually wrapped load_mupa_file
but it might be more advantagious to write a general wrapper.

I also only have the simplest test case included, to test to make sure
that the environment can actually run python test cases.