Add special extension bundle loading and bundle includes.
Review Request #7991 — Created Feb. 23, 2016 and submitted
This adds the ability to specify one or more default bundles to load when calling the load_extensions_css and load_extensions_js template tags. Each now take a third parameter, specifying a comma-separated list of It adds a third parameter bundle IDs to load, defaulting to "default" as before. By allowing the default to be changed, pages can load certain specially-defined bundle IDs, like "tests".
Made use of these in an upcoming Review Board change.