Convert MovePage to startAtomic()/endAtomic()

Convert MovePage to startAtomic()/endAtomic()

* This makes moves of a page and its subpages atomic
  as one operation. Note that $wgMaximumMovedPages
  already bounds the number of page rows changed.
* The TitleMoveComplete hook will fire for all
  titles after the operation rather than after
  each title move.
* Remove LocalFile comment about it commiting the
  transaction because LocalFile::lock()/unlock()
  check trxLevel() and reference count.

Change-Id: Ic7f6964f94f0b0f0bedc27012e5b5b012a4afdb2