Univention Corporate Server 4.0 erratum 147 (bugfix)

This update fixes the following issues:
* A memory leak caused by parsing XML documents has been fixed.
* Some unused code has been removed.
* A display error of the icon for VNC access in Firefox has been corrected 
  in the UMC module.
* An error in the grid of the UMC module resulted in an endless refreshing
  loop of the grid if no connection was available. This has been adjusted.
* Orphaned widget references in the UMC module that would lead to a growing
  memory consumption in the browser are now cleaned up.
* The Debian-installer does no longer set locale/keymap, which caused the
  join script to use en-us as default keyboard layout. This has been fixed.