PR for _sass branch

This branch is now ready for prime time. Thanks to all involved:
@gregrickaby @bradp @hugobaeta @obenland @sabreuse @MichaelArestad 
(and anyone else involved - you rock, thanks!)

Relates to: #548 
Sass processor with `style=compressed` flag will remove this comment making it useless for `wp-admin`.

Please start comment with :
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