In TMultiGraph::Add(TMultiGraph *multigraph, Option_t *chopt)
If "chopt" is defined all the graphs in "multigraph" will be added with the "chopt" option.
If "chopt" is undefined each graph will be added with the option it had in "multigraph".
Fix off by one error in out-of-bound check.

Avoid reading pass the end of an array in TTreeFormula.
This fixes http://root.cern.ch/phpBB3/viewtopic.php?t=16969.