Merge branch 'grid-enhance'

Many enhancement to wxGrid UI: fix redraw and (some) flicker bugs; fix
bugs with mouse handling; improve editors positioning etc.

See https://github.com/wxWidgets/wxWidgets/pull/1902

interface/wx/grid.h

@@ -4322,6 +4322,26 @@ public:
     */
     bool CanDragColSize(int col) const;
 
+    /**
+        Return @true if column edges inside the grid can be dragged to resize
+        the rows.
+
+        @see CanDragGridSize(), CanDragColSize()
+
+        @since 3.1.4
+     */
+    bool CanDragGridColEdges() const;
+
+    /**
+        Return @true if row edges inside the grid can be dragged to resize the
+        rows.
+
+        @see CanDragGridSize(), CanDragRowSize()
+
+        @since 3.1.4
+     */
+    bool CanDragGridRowEdges() const;
+
     /**
         Return @true if the dragging of grid lines to resize rows and columns
         is enabled or @false otherwise.