Univention Corporate Server 3.2 erratum 39 (bugfix)

This update fixes several issues:
* If a component is blocking a release update and this component part of the
  App Center, link to the app instead of showing a cryptic error message
* Fixed the error handling in case the UMC server is restarted during an
  update
* Fixed a JavaScript error when installing package updates
* The updater now uses the individual user agent string for more HTTP requests
* univention-add-app now works through proxies
* Fixed an error in the documentation of the option --latest of
  univention-add-app