Fire notification hook when promoting sandbox to full project

Because of the way hook_nodeapi() works (we can't see "before" and "after" values in the 'update' $op), it's difficult to accurately detect when a sandbox is promoted to a full project. I started hacking in a hook_form_alter(), but that has its own potential annoyances due to node_load() caching. Then I realized it could all be solved with what I'm hoping is a very reasonable hook fired in project_promote_project_form_submit(), notifying listeners that a promotion has occurred and passing along the relevant project node. So I did that, and I've now tested this through - it works swimmingly for triggering the repo manager, which is what I need to do (rename/relocate the repos on disk when a promotion occurs).

Two line patch. One line's a comment. Pretty please? :)