Revision 31207

merge from  https://root.cern.ch/svn/root/branches/dev/mathDev/hist/hist  up to revision 31170 
from David and myself 


Summary of major changes: 

- TFitResult, TFitResultPtr

  - add new class TFitResult which extend FitResult with TNamed for the I/O. The result of the fit , including covariance and correlation matrix, minos errors, etc... can then be stored  in a file
  - add a class TFitResultPtr which behaves like a pointer to TFitResult and can be converted to an integer. This class is now returned by TH1::Fit and TGraph::Fit. By default the class contains only the returned integer status of the fit. If option "S" is used the class contains a pointer to TFitResult which can be retrieved using the -> or * operators (like a smart pointer)
The conversion to int provides backward compatibility with the old signature ( int TH1::Fit )

- TH1, TGraph, TGraph2D, TMultiGraph
  change from int Fit(....)  to TFitResultPtr Fit(.....)
  remove internal function DoFit  
  
- THnSparse

  add functionality for fitting a sparse histogram. Default method is the likelihood one. Chi2 can be used with the new option "X"

- FOption

 - add some new options for fitting: 
 
     "S" for storing the fit resul
     "X" for forcing chi2 fit in case of THnSParse
     "EX0" for neglecting errors in X when fitting TGraphErrors

- WrappedMultiTF1

 - make the wrapper for TF1 multi-dim function implementing the gradient interface 

Minos changes: 

 TH1: 
  - add check of compatibility for each bins when using Add on variable bin histograms

 TH3: 
 - fix a bug in setting the entries for a projected 2d profile when using weights
 THNSParse: 
 - set also the entries (and reset statistics) in the projected sparse histogram

 TFormula: 
 - define the number for the 2d function like xygaus or xylandau

 HFItInterface: 
  improve filling data for histograms (add support for bin volume normalization)
  add initialization for exponential and 2d gaus functions