Handling ValuesQuerySet

  ValuesQuerySet are used when the client code is using the .values()
function to retrieve a specific set of attributes from the objects. In
such case we really can not and don't want to the query_time or do the
type check.
Correctings a type in ValuesQuerySet and adding import
Merge pull request #13 from swisscom/handling-of-valuesqueryset

Handling ValuesQuerySet