degenerate faces where responsible for some self intersections, so we remove
them after collapses and flips
the function that checks that no triangle gets inverted by a flip has also
been fixed
we had to check both the 1-ring of source(h) and target(h), even though those
vertices got the same coordinates
The common faces in their rings were degenerate, but their normals had all to
be checked for consistent orientation
also add more debugging code
Jane Tournois
d56e54ec6f