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

[wmtan]

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.

[cmsbuild]

A new Pull Request was created by @wmtan for CMSSW_7_1_ROOT6_X.

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

It involves the following packages:

CondCore/ORA

@ggovi, @cmsbuild, @apfeiffer1, @Degano, @nclopezo can you please review it and eventually sign? Thanks.
@ghellwig this is something you requested to watch as well.
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