Make wxGrid::GetBatchCount() const

There is really no reason for this simple accessor not to be const.

include/wx/generic/grid.h

@@ -1235,7 +1235,7 @@ public:
     void     BeginBatch() { m_batchCount++; }
     void     EndBatch();
 
-    int      GetBatchCount() { return m_batchCount; }
+    int      GetBatchCount() const { return m_batchCount; }
 
     virtual void Refresh(bool eraseb = true, const wxRect* rect = NULL) wxOVERRIDE;
 

interface/wx/grid.h

@@ -4991,7 +4991,7 @@ public:
         (yet) matching calls to EndBatch(). While the grid's batch count is
         greater than zero the display will not be updated.
     */
-    int GetBatchCount();
+    int GetBatchCount() const;
 
     /**
         Returns the total number of grid columns.