#727 package repository extension now supports message based plugin API

Have you tried this with a task plugin? Won't this fail? I mean, if you have a task plugin as well, registered, then this can cause a problem, right?

Every plugin load will call the ```pluginLoaded``` method in this class. That will, in turn, call this method. This call to ```packageAsRepositoryExtension.getRepositoryConfiguration()``` will (I think) fail, because it will send a JSON request to the task plugin.

The code on line 51 above (earlier code) was getting the metadata only for plugins which have a reference of PackageMaterialProvider.class. What is the equivalent for JSON messaging based plugins? How are the capabilities of the plugin verified?

Maybe I missed something?