remove_short_edges(), and remove_percent_shortest_edges().   I also reworked
the graph creation functions to make them a little more versatile.  Now
you can use infinite distances to indicate that certain nodes are not
connected at all.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403657