Segmentation fault fix.

I pulled this copy from pypi and fixed a segmentation fault that was occuring for all hash functions due to the size_t type being used for length in python 2.7 (python 2.x passes in an int by default for s# vars). I modified the type to Py_ssize_t type to ensure compliance with 3.x and compatibility with 2.x. So this should work on 2.x and 3.x now without a problem.

Best,
Matt