Added clatrix dep, for experimentation.
Changed add-families-wts-to-mat! make 2-way links

Previous version only made links for each pair of mapnodes in a family,
in a single order.  This in effect creates 1-way links, but we need
2-way links.  Now add-families-wts-to-mat! uses both orderings of
mapnode pairs to increment link weights.