[turba] Class definition of Horde_Core_Ui_VarRenderer_Turba not found. after upgrade to 4.2

[Sandra Weddig]

My Horde installation yields the following if I try to search a contact
inside webinterface:

Ein schwerer Fehler ist aufgetreten: 

Class definition of Horde_Core_Ui_VarRenderer_Turba not found.

1. Turba_View_List->__construct() /opt/horde/turba/search.php:188
2. Horde_Core_Ui_VarRenderer::factory() /opt/horde/turba/lib/View/List.php:127