from Gabriel: 

   - through use of RetrieveBinContent / GetBinErrorSqUnchecked and code cleanup -> achieved a 1.5x-2x speedup for TH1::Chi2Test
   - reverted changes made to GetBinContent methods for 2 or 3 dimensions: these should still call TH1::GetBinContent since it is possible to have to call BufferEmpty
   - made TAxis::GetLabels const -> as a consequence, deleted unnecessary const casts in TH1 code
   - replaced GetBinError(bin) * GetBinError(bin) with GetBinErrorSqUnchecked(bin) in TH1::Merge


git-svn-id: https://root.cern.ch/svn/root/trunk@48400 27541ba8-7e3a-0410-8455-c3a389f83636
from Gabriel:

- coverity fixes in TUnfoldBinning.cxx : 48349, 48359 -> 48369, 48475) 
 committed in http://root.cern.ch/viewvc?view=rev&revision=48400

- code cleanup  in TH1 (Eval, GetIntegral)


git-svn-id: https://root.cern.ch/svn/root/trunk@48401 27541ba8-7e3a-0410-8455-c3a389f83636