Add CanOverflow function to wxGridCellAttr

Add function to determine whether the cell will draw the overflowed text
to neighbour cells. Note that only left aligned cells currently can overflow.

src/generic/grid.cpp

@@ -645,6 +645,13 @@ wxGridFitMode wxGridCellAttr::GetFitMode() const
     }
 }
 
+bool wxGridCellAttr::CanOverflow() const
+{
+    int hAlign;
+    GetAlignment(&hAlign, NULL);
+    return GetOverflow() && (hAlign == wxALIGN_LEFT);
+}
+
 // GetRenderer and GetEditor use a slightly different decision path about
 // which attribute to use.  If a non-default attr object has one then it is
 // used, otherwise the default editor or renderer is fetched from the grid and