Now the channel specifier is the last parameter in a method's
parameter list with a default of 0. This is consistent with the
topological face-varying queries and also simplifies the common
case of just a single face-varying channel.
To encapsulate endcap functions from public API, add methods to
tell the number of patch points needed (GetNumLocalPoints()) and
to compute those patch points as a result of change of basis from
the refined vertices (ComputeLocalPointValues()).
ComputeLocalPointValues takes contiguous source data of all levels
including level0 control vertices.
