changed: allow libname for hidden extension points

needed for repository add-ons
changed: allow calling non-plugin extension points as plugins
added: support python based add-on installers

these are called as a vfs plugin with parameters.
reindent
Merge pull request #2816 from cptspiff/python_installers

Python based add-on installers
Merge pull request #1 from xbmc/master

June 3 2013 Updates