Wikimedia Bugzilla is closed!

The WikiError class is used only in the Mail backend, very isolated areas in SpecialImport and SpecialUserrights, and a few odd bits scattered through filerepo; its documentation says it was implemented "because PHP4 doesn't have exceptions".  We now require PHP5, which *does* have exceptions, although I'm not entirely sure that they're entirely suitable for all the uses.  But between exceptions, Message string errors, and Status objects, this system is completely duplicated and extremely inconvenient to keep around; the mail system in particular creeps all over the place.