backfollow bug is fixed

[Mark S. Miller <mark>]

It was (of course) trivial once found.  The good news is that I've now
got things set up to do automated regression tests involving febe, as
well as linked in.  Both use the same *u.cxx file, and the same *r.txt
file.  The regression testing sequence runs the tests in the "fe"
directory both ways and checks them against the same reference files.