Get rid of StubUser. Constructing a user object isn't quite as intensive as it once...

Get rid of StubUser. Constructing a user object isn't quite as intensive as it once was. It actually takes more time using the StubUser (construction + unstub on first call) than just initializing User::newFromSession() from the start. Either way, the real overhead starts when you start calling methods (for the nitpicky, the optimization was only about 20µs. The real gain here was eliminating a StubObject)