* Further work on rev_deleted; changed to a bitfield with several data-hiding

* Further work on rev_deleted; changed to a bitfield with several data-hiding
  options. Not yet ready for production use; Special:Revisiondelete is
  incomplete, and the flags are not preserved across page deletion/undeletion.
  To try it; add the 'deleterevision' permission to a privileged group.
Also split some functions from GlobalFunctions to XmlFunctions.php, added
some convenience functions for building form controls, some more Linker
conveniences for formatting various types of standard link clusters.