fix ROOT-5241 by implementing the option 'noclear'.
THStack
remove workarounds that are no longer needed (ROOT-5623)
remove workarounds that were there only to support the now removed workaround in constructors
make sure that we get an error report and not a crash
Implement a new function TH1;:Chisquare to compute the chi-square of an histogram given a function
(see ROOT-4722)

Re-implement TGraph::Chisquare as TH1::Chisquare using the ROOT::Fit::Chi2FCN class.
Add also option "R" to compute the chi2 in the given  function range (by default the range now is given by the data object - graph or histogram as it is done in Fit)

Conflicts:
	hist/hist/inc/TH1.h
	hist/hist/src/HFitImpl.cxx
	hist/hist/src/TH1.cxx
Change TGraph::Chisquare to pass a non-const TF1 pointer, since TF1::Eval is not const