Make wxGridSelection::IsInSelection() const

There is really no reason for it not to be.

include/wx/generic/gridsel.h

@@ -28,8 +28,8 @@ public:
                     wxGrid::wxGridSelectionModes sel = wxGrid::wxGridSelectCells);
 
     bool IsSelection();
-    bool IsInSelection(int row, int col);
-    bool IsInSelection(const wxGridCellCoords& coords)
+    bool IsInSelection(int row, int col) const;
+    bool IsInSelection(const wxGridCellCoords& coords) const
     {
         return IsInSelection(coords.GetRow(), coords.GetCol());
     }

src/generic/gridsel.cpp

@@ -55,7 +55,7 @@ bool wxGridSelection::IsSelection()
     return !m_selection.empty();
 }
 
-bool wxGridSelection::IsInSelection( int row, int col )
+bool wxGridSelection::IsInSelection( int row, int col ) const
 {
     // Check whether the given cell is contained in one of the selected blocks.
     //