Support bare interpolation in attribute selectors.

Closes #331
Declare invert().
Merge branch 'stable'
Add null literal.
Make keyword argument parsing stricter.

Closes #328
Merge remote branch 'origin/master'

Conflicts:
	doc-src/SASS_CHANGELOG.md
Merge remote branch 'origin/stable' into stable

Conflicts:
	doc-src/SASS_CHANGELOG.md
Merge branch 'stable'
Fix Dir.glob with backslash paths on Windows.
Use my listen repo for the time being.

My repo contains a few bug fixes that aren't in the main repo yet.
Fix listener for nested dirs.

Closes #362
Merge branch 'stable'
Replace the Listen plugin with an implementation of the Listen callback

Conflicts:

	lib/sass/plugin/listener.rb
	vendor/listen
Fix some errors.
Fail loudly when watching non-existent files.
Style changes.
Don't force polling.

We want to be able to use other Listen plugins if we're using the
Listen gem.
Merge branch 'listen' into stable

Closes #377
Merge branch 'stable'
Fix rake package/install on Ruby 1.9.

Closes #365