- Optimize THistPainter::PaintErrors such that the vertical and horizontal

  lines go to the marker without a gap.

- New options to draw contours for 2-d histograms.
  The contour option "CONT" is now a pure 2-D option. It is not based
  on the surface/lego algorithms.
  This option computes now a set of points stored in a list of TGraph objects.
  The points in the TGraph are sorted, such that one contour can be drawn
  with one fill area. In addition, when the option "List" is specified,
  the list of generated TGraph objects is stored in a TObjArray with the
  name "contours". This TObjArray is accessible via gROOT->GetListOfSpecials().
  When the option "CONT" is used, one can superimpose new contours on top
  using the options "CONT1", "CONT2" or "CONT3".
  The previous algorithm used by the option "CONT" is still available
  as option "CONT4".
  For example, the following call
     h2->Draw("contzlist");
  produces:
    - a picture with surface colors to delimitate each contour
    - the color palette.
    - a list of the boundary points for each countour.
  The points used to draw the contours are saved in the TGraph format
  and are accessible in the following way:
  TObjArray *contours =
           gROOT->GetListOfSpecials()->FindObject("contours")
  Int_t ncontours = contours->GetSize();
  TList *list = (TList*)contours->At(i); //where i is a contour number
  list contains a list of TGraph objects. For one given contour, more than
  one disjoint polyline may be generated. The number of TGraphs per
  countour is given by list->GetSize().
  Here we show only the case to access the first graph in the list.
    TGraph *gr1 = (TGraph*)list->First();


git-svn-id: http://root.cern.ch/svn/root/trunk@453 27541ba8-7e3a-0410-8455-c3a389f83636