Don't call TClass::New for each container element

This fixes the huge time consumption for the ROOT6 relvals,
In the conditions code, TClass::New was called for each element of a collection, which is not a good idea for over 100K emements.  This fix calls it once for each container and reuses the memory.
This is a HUGE time savings.
Please merge ASAP, and the ROOT6 IB's should actually finish in a finite amount of time.