add Chebychev polynomials
(merge from trunk 47229, 47491,47595)

add also TH1::GetStdDev and TMath::StdDev  
(merge from trunk 47595)


git-svn-id: https://root.cern.ch/svn/root/branches/v5-34-00-patches@48567 27541ba8-7e3a-0410-8455-c3a389f83636
add missing patch from previous commit (r 48567)


git-svn-id: https://root.cern.ch/svn/root/branches/v5-34-00-patches@48568 27541ba8-7e3a-0410-8455-c3a389f83636