OS X: minor wxDataViewCtrl issues

[Robert Roebling]

  Hi (Hartwig and Stefan),

wxDataViewCtrl under OS X already looks great, but I spotted
three minor issues. 

a) If the mouse is over the column header the mouse cursor
   does not change to indicate resizing. No idea if that
   is controlled by an option or if we accidentally override
   a certain setting

b) I just changed the hilite mode to FillHilite as it is
   under GTK+ and Windows and I think we should change the
   code in the custom renderer to automatically draw the
   background. This should probably be done in 
   src/mac/carbon/databrow.cpp , line 616 before calling
   the custom renderer's Render(). According to the docs,
   this should be a rect with the following colours:

" [...] the highlight color in Mac OS X v. 10.3 for active items is
  kThemeBrushAlternatePrimaryHighlightColor and for inactive items the
  color is kThemeBrushSecondaryHighlightColor."

c) The triangles indicating a tree branch are not centered.
   I wonder if actually the trianglew are right but everything
   else is accidentally moved a few pixels.

Thanks,

  Robert