Use Py_ssize_t for murmur3 key len
libev C extension fixes from static analysis

I used the gcc-python-plugin's gcc-with-cpychecker tool as
described here:
http://gcc-python-plugin.readthedocs.org/en/latest/cpychecker.html#gcc-with-cpychecker

Note that the checker does still have some bugs, so it will raise errors
with the current code.