Update to include "Implement Clone for histograms".

https://github.com/cms-sw/root/commit/0e440ee5f066ea63115eb843366bd23d5c40fe42.
Merge pull request #1127 from degano/root_53418_73XStable

Update to include "Implement Clone for histograms".
backport of dxr tools in to 73X stable
Merge pull request #1131 from smuzaffar/IB/CMSSW_7_3_X/stable

backport of dxr tools in to 73X stable
Move to cms-sw/root@04ffc3
Merge pull request #1136 from ktf/revert-chris-changes

Move to cms-sw/root@04ffc3
Update root and roofit to the new head.

https://github.com/cms-sw/root/commit/07f1df4138b9764c6176e6c2d57a6ace91cf2c23.
Merge pull request #1137 from degano/root_53418_updateHead

Update root and roofit to the new head.
Merge remote branch 'origin/IB/CMSSW_7_3_X/stable' into IB/CMSSW_7_0_X/stable