Reduce duplicate code in CssAbsolutizingTestCase
Fix #467: Remove unnecessary checks (filename in COMPRESS_ROOT, or existence of file) in CssAbsoluteFilter
Update usage.txt
Merge pull request #539 from alimony/patch-1

Fix typo
Merge pull request #471 from agriffis/CssAbsoluteFilter-skip-filename-check

Remove unnecessary filename and existence checks in CssAbsoluteFilter
Update test_css_no_hash pursuant to changes in CssAbsolutizingTestCase from 626bc52007378bedb39a40f4a0334f0e20ba49f6.
Types at readme (-engine should be --engine)
Merge pull request #540 from lukaszb/patch-2

Types at readme (-engine should be --engine)
Apply shell quoting to infile/outfile. #536