Mark THreadSafeRegistry as being thread safe

The declaration of the static needed a CMS_THREAD_SAFE designation in order to have the static analyzer not complain about it.
add edm::RunningAverage to  thread safe class list
Merge pull request #6380 from Dr15Jones/markThreadSafeRegistryAsThreadSafe

Mark THreadSafeRegistry as being thread safe
Merge pull request #6386 from gartung/clangSA-skip-edm-runningavg

add edm::RunningAverage to  thread safe class list
Merge remote branch 'origin/CMSSW_7_3_X' into CMSSW_7_0_X