Major Description
This patch introduces a configuration parameter in the properties file "shindig.gadget-rewrite.externalize-feature-libs"
When this parameter is set to true, RenderingGadgetRewriter will gather all features requested by the gadget and simply add them to the set of extern libraries. As a result, the browser will see <script src='http://shindig-host/gadgets/js/feature1:feature:2:feature3'><script> and get the features specified in the path.
When this parameter is set to false (the default), RenderingGadgetRewriter will do what it normally does. Inline features requested by the gadget.
The benefit of setting externalize-feature-libs to true is that browsers can cache features requested by the gadget.