Univention Corporate Server 4.2 erratum 617 (extended maintenance)

This update addresses the following issues:
* Proxy Auto-Configuration file can define localhost access to be proxied
  (CVE-2018-18506)
* Memory safety bugs fixed in Firefox 66 and Firefox ESR 60.6 (CVE-2019-9788)
* Use-after-free when removing in-use DOM elements (CVE-2019-9790)
* Type inference is incorrect for constructors entered through on-stack
  replacement with IonMonkey (CVE-2019-9791)
* IonMonkey leaks JS_OPTIMIZED_OUT magic value to script (CVE-2019-9792)
* Improper bounds checks when Spectre mitigations are disabled
  (CVE-2019-9793)
* Type-confusion in IonMonkey JIT compiler (CVE-2019-9795)
* Use-after-free with SMIL animation controller (CVE-2019-9796)
* IonMonkey MArraySlice has incorrect alias information (CVE-2019-9810)
* Ionmonkey type confusion with __proto__ mutations (CVE-2019-9813)