This makes several methods that didn't have any effect before work
correctly, including SetToolTip(), whose effect is now shown in the
sample, but also SetCursor() and SetLayoutDirection().
Some methods would now actually work too well: SetForegroundColour() and
SetBackgroundColour() implementations in wxCompositeWindow apply to all
sub-windows, but in wxDataViewCtrl they are only supposed to affect the
items, but not the header, so we need to override them to prevent the
base class version from being used. It is still preferable to explicitly
disable these two methods and inherit all the other ones (including any
possibly added in the future) from wxCompositeWindow to implementing all
the methods manually in wxDataViewCtrl itself.
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