Use ASSETS_DEBUG instead of DEBUG

Django sets DEBUG to False while running unit tests. Thus, DEBUG is not a good indicator for staticfiles usage, but ASSETS_DEBUG is a better one.

This problem is described in https://github.com/miracle2k/django-assets/issues/3
Make tests actually import staticfiles finders

staticfiles finders were not being loaded (and silenced by try/except)
since the settings are not yet configured at the point of import.
Import multiprocessing to help with atexit errors

http://bugs.python.org/issue15881#msg170215
https://groups.google.com/forum/#!msg/nose-users/fnJ-kAUbYHQ/_UsLN786ygcJ
There is no self in assert_raises_regexp
Make sure template test uses some unicode
Tests needed to be changed to use ASSETS_DEBUG.
"Merge pull request #40 from rassie/fixes\n\nAssorted fixes"
Don't use smart_text(), too modern.
Fix template filter.

The internal filter pipeline prefers unicode objects on Python 2
as well.