Bug: If a tag edit failed because it contained a metatag that raised an
exception, then a new post version would be created even though the edit
didn't go through. This could happen if the newpool:, fav:, favgroup:,
disapproved:, status:active, or status:banned metatags failed (for
example, because of a privilege error).
Fix: Silently ignore all errors raised when applying metatags. This way
the edit will always succeed, so erroneous post versions won't be created.