gEDA-user: [pcb] global puller

[DJ Delorie]

Most likely, it was looping.  There are three failure modes:

First, it loops trying to move things around.  I can't tell exactly
what or why it's doing it (there's way too much math to catch just one
iteration easily) but it tends to just sit there schizophrenically
wiggling the traces.

Second, it sometimes does loops around obstacles instead of just
gracefully bending around them.

Third, it runs out of undo space.  I might have fixed this somewhat by
swapping ends (part of the math) locally instead of through undo.