Clamp integer scalars in InterpolateTuple().

The InterpolateTuple() function was seeing an integer overflow
when used from vtkButterflySubdivisionFilter, and probably had
undetected overflow issues elsewhere.  Adding a clamp to the
interpolation code for integer types protects against overflow.

Change-Id: Ibd6ab7f79d514dbb9ea2d055cc299273b7490f7b