[Grok-dev] Adding Valueindex

[Sebastian Ware]

Could we consider adding ValueIndex to grok.Index? I don't know if you  
need tests for this (looks like the SetIndex lacks tests), but the  
change is trivial:

grok/index.py:

   from zc.catalog.catalogindex import ValueIndex
   class Value(IndexDefinition):
       index_class = ValueIndex

Mvh Sebastian