Added ReusableObjectHolder class

[Dr15Jones]

The class ReusableObjectHolder is a thread safe caching
system which allows one to create objects as needed and
be able to reuse those objects once they are no longer in
use.

[cmsbuild]

A new Pull Request was created by @Dr15Jones (Chris Jones) for CMSSW_7_2_X.

Added ReusableObjectHolder class

It involves the following packages:

FWCore/Utilities

@cmsbuild, @Degano, @Dr15Jones, @ktf, @nclopezo can you please review it and eventually sign? Thanks.
@wddgit, @wmtan this is something you requested to watch as well.
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[Dr15Jones]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_2_X IBs unless changes or unless it breaks tests.

[cmsbuild]

+1
Tested at: a357fb5
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-4853/527/summary.html

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_2_X IBs unless changes (tests are also fine).

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-4853/527/summary.html