Made static nWarn thread-safe via std::atomic

[Dr15Jones]

nWarn is used to only allow at most 5 Info messages to be sent when particilar functions are called. The static int was changed to a static std::atomic<int> so the increment is done in a thread safe manner.
The thread-safety checker says this indirectly affects 116 modules.

[Dr15Jones]

@ktf this is just a trivial technical change

[cmsbuild]

A new Pull Request was created by @Dr15Jones (Chris Jones) for CMSSW_7_0_X.

Made static nWarn thread-safe via std::atomic

It involves the following packages:

TrackingTools/GsfTracking

@nclopezo, @smuzaffar, @thspeer, @slava77 can you please review it and eventually sign? Thanks.
@gpetruc, @cerati, @GiacomoSguazzoni, @rovere 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.
@ktf you are the release manager for this.

[slava77]

+1

tested (sign263) in CMSSW_7_0_X_2013-10-26-1400
#1187 3739654
#1186 8c7ae33
#1180 e5f07bd
no diffs as expected

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next IBs unless changes or unless it breaks tests. @ktf can you please take care of it?