Handle root6 class naming

[wmtan]

This pull request fixes the fatal exceptions seen in some of the ROOT6 relvals.
In ROOT 6, the normalized names of three types are different than those used by Reflex in ROOT5.
The code calculating the friendly class name for the purpose of branch naming did not handle the new names.
So, a class name containing Long64_t (the ROOT6 name for long long) was not translated. The framework cannot handle underscores in friendly class names, since underscore is a field separator in branch names.
This request fixes this problem, so the affected relvals will get further along.

[cmsbuild]

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

Handle root6 class naming

It involves the following packages:

FWCore/Utilities

@cmsbuild, @Degano, @Dr15Jones, @ktf, @nclopezo can you please review it and eventually sign? Thanks.
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