* Change %renderedfiles to store an array of files rendered from a given

* Change %renderedfiles to store an array of files rendered from a given
  source file, to allow tracking of extra rendered files like rss feeds.
* Note that plugins that accessed this variable will need to be updated!
  The plugin interface has been increased to version 1.01 for this change.
* Add will_render function to the plugin interface, used to register that a
  page renders a destination file, and do some security checks.
* Use will_render in the inline and linkmap plugins.
* Previously but no longer rendered files will be cleaned up.
* You will need to rebuild your wiki on upgrade to this version.