So that using this hook it's possible to prevent the move, also
providing some more context.
Also, clean error message: instead of going with "you do not have
permission blah blah" for *every* kind of error, use it only when the
error is actually about permissions, and use a generic message
otherwise.
Bug: T208907
Change-Id: I4733724075b7514e9db59e7be772d9409aa9da87
This also includes the integration test from SemanticMediaWiki that
caught this issue.
Bug: T74870
Change-Id: I699e14958ee36ec5e86278e5dc0caed2a015d9af