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.
Let's try to keep the modifications to most of the include/ files to an absolute minimum.  (exceptions are Python.h and pyport.h).  The revision we should pull from is 90928:f8921f6059edf (2.7.7 release); I see some differences, I'm not sure if they're because you added them or because this came from a different revision.  If you change anything, we should make sure to add a "Pyston change" comment to make it clear that it's an intentional difference.

The HAVE_* defines should probably go in Python.h in the "these belong in pyconfig.h" section.