Univention Corporate Server 4.0 erratum 293 (bugfix)

This update addresses the following issues:
* The list of supported message digest, encryption and key exchange
  algorithms allowed by the SSH daemon can now be configured through the
  new UCR variables 'sshd/MACs', 'sshd/Ciphers', and 'sshd/KexAlgorithms'.
* The insecure SSH protocols 'rsa1' and 'dsa' have been disabled. They can
  be re-enabled through the new UCR variables 'sshd/Protocol' and
  'sshd/HostKey'.
* Fix handling of UCR variable 'sshd/banner'.