* messages can now be edited/deleted (explicit permissions need to be given)
* topics can be locked so that no reply can be added (only by users allowed to edit messages)
* topics can be marked as sticky so that they always appear at the top of the list (only by users allowed to edit messages)

git-svn-id: https://svn.redmine.org/redmine/trunk@926 e93f8b46-1217-0410-a6f0-8f06a7374b81