pickle should be binary instead of ascii

pickle protocols higher than 0 are binary formats and
should be written as such, per the warning in
https://docs.python.org/2.7/library/pickle.html#usage
make gzip binary status explicit

Python gzip docs say that modes missing 'b' get it added silently.
Better to make the binary mode more visible.
Merge pull request #57 from fiendish/master

pickling in ascii mode can corrupt metadata