Add fpclassify() and FP_* constants to math.pxd
Add fpclassify() and FP_* constants to math.pxd

Closes #2514.

cython/cython,da-woods/cython,scoder/cython,cython/cython,cython/cython,da-woods/cython,scoder/cython,da-woods/cython,scoder/cython,scoder/cython,da-woods/cython,cython/cython