Univention Corporate Server 4.1 erratum 319 (bugfix)

This update addresses the following issues:
* The DHCP options mapping was fixed so that multiple values can be provided.
* The "failover peer" property description has been renamed into "failover
  peer configuration".
* Some univentionObject object classes are added to automatically created
  objects.
* The DHCP "netmask" property has been renamed into "address prefix length".
* DHCP Pools may now be created underneath of shared subnets.
* DHCP Pools may now be created via the DHCP UMC module.
* Positions and types of superordinate objects are now validated before
  creating objects.
* The UMC modules don't crash anymore if the UCR variable
  directory/manager/web/sizelimit is empty.