Moar tests

So I started working on py3k support, but since I was re-reminded of @brutasse's #70, I rebased and deleted those commits. Additionally, due to #98, which I also did, I rebase deleted those commits as @amosshapira took care of that first :)

Anyways, this brings up the total test coverage of whisper.py up from 67 --> 86%. I'll be slowly continuing to update this, but it can be merged now.
FYI the code was buggy before. If you set `CACHE_HEADERS=True`, ran `whisper.info()` on a whisper file, set `CACHE_HEADERS=False`, and then used `whisper.resize()` or something to change the archive in the same python process (like a test that re-uses the same archive name over multiple tests), it will always and only use the cached version.

That behavior is blatantly broken as you shouldn't use the cache if CACHE_HEADERS is False. This was to prevent it from happening again.