[bug 779502] Fix ES_LIVE_INDEXING issues

* overrides the setting if you do ./manage.py esreindex figuring
  if you're running that on the command line you really mean it
  for realz srsly.
* puts a big warning note in the admin figuring it's hard to
  override it in the admin without fiddling with a lot of code, but
  a warning is helpful.