Move to py-bcrypt 0.3.

py-bcrypt 0.2 has a security problem, and has been pulled from PyPI. See https://code.google.com/p/py-bcrypt/source/detail?r=3bc365ff43736d26ff37e9f2a4084f37b381b569 for details.
Merge pull request #52 from Osmose/master

Move to py-bcrypt 0.3.