Univention Corporate Server 4.0 erratum 43 (bugfix)

* Fixed setting of userexpiry when a user account is disabled.
* Fixed removal of the account expiry date of a user.
* The user properties CtxBrokenSession and CtxReconnectSession now
  have default values. They prevented changes via UMC when not having
  sufficient LDAP permission to change these attributes. Especially
  affected were User Password Admins and the users/self module.
* The univention.admin.uexception.base class provides now more detailed
  information about the error cause.
* Error handling of UDM modules has been improved by adding default methods
  which contain information about the current edited object type.
* The "Release" policy has been renamed into "Automatic updates" and its
  property descriptions have been improved.
* Remove references to the network object when deleting it.