Backport of xz, root and rootfit from 72X
Merge pull request #812 from nclopezo/backport-xz-root-roofit

Backport of xz, root and rootfit from 72X
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