xroofit → histfactory Relation

File in roofit/xroofit	Includes file in roofit/histfactory
src / xRooNode.cxx	inc / RooStats / HistFactory / FlexibleInterpVar.h
src / xRooNode.cxx	inc / RooStats / HistFactory / ParamHistFunc.h
src / xRooNode.cxx	inc / RooStats / HistFactory / PiecewiseInterpolation.h