Add CMSSW_7_3_DEVEL_X IB.
Remove CMSSW_7_2_DEVEL_X.
Update root to include global functions list lock and clang fix.

See also cms-sw/root#31 and cms-sw/root#30.
Merge pull request #1082 from degano/root_fixes_72XStable

Update root to include global functions list lock and clang fix.
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
Merge remote branch 'origin/IB/CMSSW_7_2_X/stable' into IB/CMSSW_7_0_X/stable