New recipe for compass 960 plugin AND fix for compass recipe and SCSS syntax

I just sent a pull request with a recipe for compass_960_plugin and a modification for the compass.rb recipe, to generate a stylesheet based on the sass/scss selection.
I hope it helps!

This is the url of the pull request.
https://github.com/RailsApps/rails_apps_composer/pull/51
