make GctRawToDigi inherit from edm::one::producer becuase it accesses non-const static vars.
Merge pull request #2130 from gartung/EventFilter-GctRawToDigi-GctRawToDigi-edm-one-producer

Multithreading fixes -- Make GctRawToDigi inherit from edm::one::producer.
Merge remote branch 'origin/CMSSW_7_1_X' into CMSSW_7_0_X