Always add '-m32' or '-m64' to module cache key

This is to avoid loading modules compiled with one architecture from a
Python with a different one.
Add Python bitwidth in config.compile_dir.

Also move local_bitwidth to gof/compiledir, import it directly in
theano.gof, and use the latter path.
Pep8 / Pyflakes
Address comment in code review
Merge pull request #1271 from lamblin/arch_in_cache

Always put arch bitwidth in cache