Univention Corporate Server 4.2 erratum 544 (extended maintenance)

This update addresses the following issues:
* Incorrect reuse of client certificates (CVE-2016-7141)
* escape and unescape integer overflows (CVE-2016-7167)
* printf floating point buffer overflow (CVE-2016-9586)
* Heap-based buffer overflow via integer overflow in
  curl_sasl.c:Curl_sasl_create_plain_message() (CVE-2018-16839)
* Heap-based buffer over-read in tool_msgs.c:voutf() allows for information
  disclosure and crash (CVE-2018-16842)