fixes for #155233, #141518, #155073, #154960, coder module warning fixes, new status message to notify people they were logged off intentionally when their uid is downgraded to 0

fixed the following bugs:
  option to invalidate existing sessions: http://drupal.org/node/79361
  Doesn't work in PostgreSQL: http://drupal.org/node/109874
  won't disconnect current session: http://drupal.org/node/101974