It's hopefully no longer needed, at least not needed for as long as
single ptex face corresponds to a single patch which should be always
correct for uniform subdivisions as far as i know.
Implementation is less optimal compared to non-opensubdiv drawing but
it is now as good as we can do it without affecting on how patches are
being created by OpenSubdiv.
This includes C-API bindings in intern/opensubdiv and CMAke module
which finds the OpenSubdiv library. This filea are not in use so
far, making it a separate commit to make actual integration commit
more clear.
