Item12566:Item11700: protect comments from being edited by others

   * fixed error reporting using pnotify now
   * reject commenting when discussion is already closed
   * added example how to display all unapproved comments in a web
   * added docu how to render an rss feed of all comments in a web



git-svn-id: http://svn.foswiki.org/trunk@16860 0b4bb1d4-4e5a-0410-9cc4-b2b747904278