Merge pull request #1414 from HapeMask/py3k-fixes

Use NpyCapsule instead of PyCObject for py3k compat.
fix tests/crash on python 3
Merge pull request #1415 from nouiz/py3

fix tests/crash on python 3
Fixed #defines to work with npy_3kcompat and bytes.
npy_3kcompat redefines old PyString_X to use bytes, but this breaks
compatibility with python code expecting new strings. The solution is to
use PyUnicode wherever possible instead of PyBytes.
Signature for capsule destructor changed in py3k.