Update root to use fix for fIsAMethod thread safe.

See also cms-sw/root#27.
Merge pull request #1067 from degano/root_isamethod_fix_72X

Update root to use fix for fIsAMethod thread safe.
Merge remote branch 'origin/IB/CMSSW_7_2_X/stable' into IB/CMSSW_7_0_X/stable