Univention Corporate Server 4.3 erratum 252 (bugfix)

This update addresses the following issue(s):
* Allow to customize portal with about page
* It is now possible to define custom categories for the portal.
* User Templates now have access to the alphanum option.
* For performance reasons, UDM stores the last used value of uidNumber
  and gidNumber in an LDAP object in the univentionLastUsedValue
  attribute. Usually these two values are monotonously increasing with
  automatic assignment. When manually specifying the uidNumber/gidNumber
  when creating an object, however, this value could jump back to a lower
  value and previously used and now free values could be reused if
  necessary. This behavior has now been disabled. univentionLastUsedValue
  is now monotonously increasing.
* The visibility of a portal entry object can now be restricted
  to multiple groups instead of just one.
* The search filter generated for boolean and multi-value properties
  of UDM objects was not correct. This has been resolved.
* Fix a traceback during portal assignment at computer objects when a
  settings/portal object is created.