r3140: * try to ensure consistent usage of the username map.

r3140: * try to ensure consistent usage of the username map.
  Use the fully qualified DOMAIN\user format for 'security = domain|ads'
  and apply after authentication has succeeded.

* also change fill_domain_username() to only lowercase the username
  and not the domain+username.  This was a cosmetic fix only.
  makes the output more consistent with %D and %U.
(This used to be commit 30ee2d5b0906d5cd73a8faf5170e5aebcc6d69c8)