added comments to ChainEvent::fileIndex
Multithreaded Random Number Service - Generators

First part of modifications to make the generators
use the new multithreaded random number service.
This includes all changes for the Pythia8GeneratorFilter.

HadronizerFilter and GeneratorFilter now get the random
number engine in their filter and beginLuminosityBlock
method. These engines are percolated in various ways
to where they are used. Classes are modified to only
generate random numbers in the event and beginLuminosityBlock
methods.

For Pythia8GeneratorFilter this required changes to
Pythia8Hadronizer and also the EvtGen, Photos,
and Tauola external decayers. Other generators
(for example Pythia6) are not broken by these changes,
but have not been modified yet.

HadronizerFilter and GeneratorFilter also declare
shared resources.
Merge branch 'CMSSW_7_0_X' of https://github.com/cms-sw/cmssw into threadsGeneratorRandomNumbers
Principal::getManyByType now uses same mechanisms as other gets functions

When the internals of the Principal were changed to add getByToken, all the other get functions were updated to use new lookup mechanisms except for getManyByType. This now makes it conform to the others.
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Merge pull request #1807 from wddgit/threadsGeneratorRandomNumbers

Multithreaded Random Number Service - Generators
Merge pull request #1797 from Dr15Jones/getManyByTypeUsesResolveProduct

Framework cleanups -- Principal::getManyByType now uses same mechanism as other gets functions
Merge pull request #1791 from jpata/jpata/chainevent_fileindex_comments

FWLite documentation -- Added comments to ChainEvent::fileIndex()
Merge remote branch 'origin/CMSSW_7_0_X' into CMSSW_7_0_X