Comment 3 for bug 1180302

In Thunderbird, we pass the mailbox URI as the unique identifier parameter to messaging_menu_app_append_source_with_count(), and libmessagingmenu uses this as the action name. But it seems that the new glib version is more strict, and the mailbox URI is not valid as an action name (but it ought to be valid as a unique identifier required by libmessagingmenu)