InsertNextCell and related method now return the proper vtkIdType.

Some of the methods in vtkPolyData and vtkCellTypes were returning int
when they should have used vtkIdType.

Change-Id: Icd5add3262934e355182fc9ae7a4a3ab1c7f3c47
Merge topic '0014443-vtkPolyData-InsertNextCell' into master

0b42c0e7 InsertNextCell and related method now return the proper vtkIdType.