Rename STATIC_ROOT into ROOT in some places

See https://github.com/andreyfedoseev/django-static-precompiler/pull/5#issuecomment-30833670 first, this is what I've done that allows staticfiles to work properly.

The other patch is to get `python setup.py test` to run the test case straight away (how have they been run so far?).

I am **definitely not sure** whether this is how the `ROOT` vs. `STATIC_ROOT` is supposed to be used in django-static-precompiler -- take this as an example of how to solve one problem, which may be completely incorrect approach taken.