Accept option "same" in TGraph::Draw and TGraph::PaintGraph.

The option is dummy. It is introduced for consistency with
other high level classes (TH1, TTree). It eliminates
the problem with the native option "a" of TGraph.


git-svn-id: http://root.cern.ch/svn/root/trunk@7629 27541ba8-7e3a-0410-8455-c3a389f83636