chneighbor identifies dupridges for matching by qh_matchdupridge.
In merge_r.c, qh_mark_dupridges identifies facets for merging across a dupridge.  If vertices are
nearly adjacent, qh_merge_pinchedvertices merges the vertices, otherwise qh_forcedmerges
merges the facets.  qh_forcedmerges checks for wide merges with qh_check_dupridge.

<p>It is easy to generate nearly adjacent or coincident points with rbox
option 'Cn,r,m'.  It generates n points within an r ball for each of m input sites.  For example,
the 