Import math module

Some functions are currently just stubs and I had to disable a
test which checked for a math exception because our C-API does
not support exceptions yet.
This is also yet another performance regression,
because patchpoint does not yet work for the C-API.
It looks like the Python.h include order is very specific and not just for aesthetic reasons.  Can we match the order?  ie pymath gets included right before pymem.h, and pyfpe.h gets included at the bottom.