Implement wxDV_ROW_LINES for generic wxDataViewCtrl.

Provide wxDataViewCtrl::SetAlternateRowColour() to specify the colour to use
for odd rows explicitly but determine it automatically from the background
colour if no explicit colour was specified.

Closes #12834.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70576 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/generic/dataview.h

@@ -191,6 +191,11 @@ public:
 
     virtual void EditItem(const wxDataViewItem& item, const wxDataViewColumn *column);
 
+    // These methods are specific to generic wxDataViewCtrl implementation and
+    // should not be used in portable code.
+    wxColour GetAlternateRowColour() const { return m_alternateRowColour; }
+    void SetAlternateRowColour(const wxColour& colour);
+
 protected:
     virtual void EnsureVisible( int row, int column );
 
@@ -245,6 +250,9 @@ private:
     wxDataViewMainWindow     *m_clientArea;
     wxDataViewHeaderWindow   *m_headerArea;
 
+    // user defined color to draw row lines, may be invalid
+    wxColour m_alternateRowColour;
+
     // the index of the column currently used for sorting or -1
     int m_sortingColumnIdx;