Add CMSSW_7_3_X_THREADED IB for slc6_amd64_gcc481
Add CMSSW_7_3_CLANG_X IB for slc6_amd64_gcc481
Merge remote branch 'origin/IB/CMSSW_7_0_X/stable' into IB/CMSSW_7_0_X/stable
Merge remote branch 'origin/IB/CMSSW_7_1_X/stable' into IB/CMSSW_7_0_X/stable