Some XmUGrid method's python bindings are untested

[wdolinar]

Some of XmUGrid method's python bindings are untested. One example is GetCellPlanViewPolygon there may be others.

[tchristiansen-aquaveo]

XmUGrid::GetCellPointCount() seems to be another example. The Python side thinks the method has bindings, but it actually doesn't, so UGrid.get_cell_point_count() crashes when called.