Media changelog added

There is a new media changelog now, with the flag RECENTS_MEDIA_CHANGES media changes can be requested from the getRecents()-function or the new getRecentsSince()-function, that returns all changes since a given timestamp and optionally before a given timestamp. The media upload and the XML-RPC-server have been changed to use these functions.

Additionally, the event MEDIA_UPLOAD_FINISH has been extended, it has a new $data-attribute (the 5th), that contains a boolean if the file does already exist and will be overwritten.

darcs-hash:20090118154345-074e0-5d9a90d269e86d8c6a156ecce5cf63115c827433.gz