Upgrade django-cache-machine to 0.8 (bug 883477)

https://bugzilla.mozilla.org/show_bug.cgi?id=883477

`count()`s caching is disabled in tests, this was already done before by accident, this is now done on purpose because it messes up with all the tests.

(@robhudson did most of the work, I just had to figure out what the hell was happening with the tests :)