Make GetField behavior more consitent for multivalued fields.

Before this change, the GetField#getValue() method was returning a list of values of a multivalued fields if the field values were obtained from source or if the field was stored and real-time get was used. If the field was stored but non-realtime get was used, GetField#getValue() was returning only the first element and the GetField#getValues() was returning a list of elements. This change makes behavior consistent. GetField#getValue() now always returns only the first value of the field and GetField#getValues() returns the entire list.