cffi build changes

should prevent failure to install from wheel,
due to mismatched hashes.

- move cdefs to zmq_ffi.h
- specify modulename in ffi.verify
- only use one FFI object, only call verify once
cleanup/ignore fixes

now that there are non-Cython .c files in zmq/
note pypy bundling fix
Merge pull request #600 from minrk/cffi-whl

cffi build changes