Univention Corporate Server 4.2 erratum 237 (bugfix)

This update addresses the following issue(s):
* Users from an Active Directory domain now can reset their password via the
  Self Service. To enable the feature, the UCR variables ad/reset/username
  and ad/reset/password need to be set.
* Notifications about successful password changes are shown again.
* The creation of postgresql database and users has been moved from the
  post installation script into the joinscript.