add possibility to performa a least square fir for binned data using the expected error instead of the observed one
(Pearson chi- square)
Add in Bindata methods to compute sum of weight (content) and sum of weifgt square


git-svn-id: https://root.cern.ch/svn/root/trunk@48281 27541ba8-7e3a-0410-8455-c3a389f83636
clean up the parsing of the fit option in TH1::Fit and TGraph::Fit

add new option "P" (pearson chi square) for using expected error instead of observed one when fitting

Fix a bug for the case of parameter limits (defined in TF1): [-inf,b] or [a, +inf]


git-svn-id: https://root.cern.ch/svn/root/trunk@48282 27541ba8-7e3a-0410-8455-c3a389f83636
from Gabriel: 

- multiple changes for speeding up Add / Scale methods in TH1
- replaced 3-level nested for loops with 1-level loop where possible
- replaced Get / Set BinContent with lightweight Update / Retrieve BinContent
- removed unecessary checks (e.g. TimeDisplay, CanExtendAllAxes) due to removal of Get / Set BinContent


git-svn-id: https://root.cern.ch/svn/root/trunk@48284 27541ba8-7e3a-0410-8455-c3a389f83636