* Add 'deletedhistory' permission key for ability to view deleted history

* Add 'deletedhistory' permission key for ability to view deleted history
  list via Special:Undelete. Default is off, replicating the 1.5 behavior,
  but it can be turned back on for random users to replicate the previous
  1.6 dev behavior.

Gotten a rash of requests lately to delete history items, which then still
show their forbidden details to the whole world. Until we get this sorted
out to be easier to work with, I'm disabling the view of deleted history
for non-sysops on wikimedia.