py: mp_buffer_info_t::buf may be valid, but NULL for empty objects.

This happens for example for zero-size arrays. As .get_buffer() method now
has explicit return value, it's enough to distinguish success vs failure
of getting buffer.
objarray: Implement equality testing between arrays and other buffers.
modzlibd: Decompress part of "zlib" module, based on miniz tinfl.c .
modzlib: Add tinfl.c from miniz SVN repo, r63.

The only change is line-ending convesion to LF.
tests: Add test for zlibd module.