From Axel & Lorenzo:

Fixing first and last bin default arguments. Now the default argument of:

 firstbin = 0, lastbin = -1   indicates  [0,Nbin+1]  (includes underflow/overflow)
 firstbin= 1, lastbin = -1    indicates  [1,Nbin]


git-svn-id: http://root.cern.ch/svn/root/trunk@21305 27541ba8-7e3a-0410-8455-c3a389f83636