In light of the recent security vulnerability on using localhost + port,
I've been using socket files for live hacking.  Unfortunately, these
socket files stay around after closing guile, which means this can happen:

  $ guile --listen=/tmp/guile-socket
  scheme@(guile-user)> ,q
  $ guile --listen=/tmp/guile-socket
  ERROR: In procedure bind:
  ERROR: In procedure bind: Address already in use

That's not very nice!  I really don't like having to clean up these
files by hand.... Guile should do it for me.

Fortunately, here's a patch that does just that!  It uses dynamic-wind
and cleans up the socket file, if it exists.  (But it doesn't break if
it doesn't!)