There are many cases this method will fail for non-latin languages,
but not added now since there are bugs reported on that already and results
a rewrite of the method as per UAX 31 standard.
* User::getRights(), User::isAllowed() and User::getGroupPermissions now optionally accept a namespace parameter. If not set, it will check whether the user has the right for all namespaces.
* Anything that uses Title::getUserPermissionsErrorsInternal() automatically supports per-namespace permissions. This includes Title::getUserPermissionsErrors and Title::(quick)UserCan.
* Fix tests that set User::mRights
The next step would be to change all User::isAllowed() to Title::quickUserCan or pass the namespace to User::isAllowed().