Don't really know if this is a bug but looks weird, this post is mostly so I remember to check later.
In Meeting_0.php, line 75
public function messanger_addon($arg) {
function name is misspelt, messanger -> messenger
Edit:
MeetingInstall.php, line 48,
Utils_RecordBrowserCommon::new_addon('crm_meeting', 'CRM/Meeting', 'messanger_addon', 'Alerts');
same spelling on both places so this is probably ok. (First thought it had something to do with Util/Messenger module.)
Another question, while looking through the MeetingInstall.php I noticed that install() on line 47-48 adds two addons but these are never delete in uninstall(). Don't they need to be deleted or are that done automatically when the recordset is uninstalled?