Changed statics to thread_local in EgammaTowerIsolation

[Dr15Jones]

To quickly fix the thread safety problems, the static data members
of EgammaTowerIsolation have been changed to be thread_local.
This avoids disturbing the present behavior and client APIs while
fixing the threading problems crashing jobs.
However, this should not be considered the permanent solution. Instead
the statics should become regular members and client code should
stop making temporary EgammaTowerIsolation objects and instead
keep reusing the one they make.

[Dr15Jones]

NOTE: This problem was missed by the static analyzer since the static analyzer crashed while trying to processes EgammaTowerIsolation.cc.

[Dr15Jones]

@davidlange6 This was missed by helgrind in my original run :(. So a clean helgrind does not mean thread safe.

[cmsbuild]

A new Pull Request was created by @Dr15Jones (Chris Jones) for CMSSW_7_1_X.

Changed statics to thread_local in EgammaTowerIsolation

It involves the following packages:

RecoEgamma/EgammaIsolationAlgos

@nclopezo, @cmsbuild, @anton-a, @thspeer, @slava77, @Degano can you please review it and eventually sign? Thanks.
@lgray this is something you requested to watch as well.
You can sign-off by replying to this message having '+1' in the first line of your reply.
You can reject by replying to this message having '-1' in the first line of your reply.
@nclopezo, @ktf you are the release manager for this.
You can merge this pull request by typing 'merge' in the first line of your comment.

[Dr15Jones]

@nclopezo was the test for this started?

[nclopezo]

+1
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-%20Dr15Jones:changeStaticInEgammaTowerIsolationToThreadLocal/1155/summary.html

[anton-a]

looks like the comparison job is stuck
@nclopezo can you please restrart

[slava77]

+1

for #3550 64fb651

tested in CMSSW_7_1_X_2014-04-29-0200
( test area sign361 pulls 3475 3529 3531 3550 3555 together)
no regressions .
Still had to merge manually from Chris' branch

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_1_X IBs unless changes (tests are also fine). @nclopezo, @ktf can you please take care of it?