* css url rewriting also works with absolute pats.
* added unit tests
* use urlparse rather than os.path
* removed unused imports
* added more unit tests
* don't try to clear the url cache when uploading files to the filer clipboard
* when running the unit tests, clear files generated by each test (don't leave garbage behind)
Added test for testing a css' hash and size after rewriting
Merge pull request #5 from pbs/absolute_paths

Make css url rewriting also works with absolute pats