Update CentralAuth for 1.24wmf16 cherry-picks

* Pass normalized username to GlobalRenameUserStatus
  (I5b75ecb41e8697f975963729df463225212a54f6)
* Wrap CentralAuthUser::attach in an explicit transaction
  (I715c3e2b77ba28efc36a375ee214021f1334a1d1)

Change-Id: I7fc3c25e932642c02f78fe59d10706425e983aa8