itaps-parallel Neighbor definition

[Onkar Sahni]

>
> I think neighbors 'of' dimension d are neighbors that share mesh entities
> of at most dimension d.  For example, neighbors 'of' dimension 1 are
> neighbors that share only edges and vertices.

  Then using 'd' twice in def. seems confusing. And in example, I think
neighbors 'of' dimension 2 (i.e., face, say, for finite-volume) will be
ones that have faces on inter-part boundaries (not edges and not
vertices).

- Onkar