[Cython] Conditional import in pure Python mode

[Stefan Behnel]

Stefan Behnel, 01.05.2012 21:14:
> 2) Use math.pxd as an override for the math module. I'm not sure yet how
> that would best be made to work, but it shouldn't be all that complex. It
> already works (mostly?) for numpy.pxd, for example, although that's done
> explicitly in user code.

BTW, I think it would be helpful to make the numpy.pxd cimport automatic as
well whenever someone does "import numpy" and friends, right?

Stefan