unicorn 4.3.1 - shutdown() fixes

* Call shutdown(2) if a client EOFs on us during upload.
  We can avoid holding a socket open if the Rack app forked a
  process during uploads.

* ignore potential Errno::ENOTCONN errors (from shutdown(2)).
  Even on LANs, connections can occasionally be accept()-ed but
  be unusable afterwards.

Thanks to Joel Nimety <jnimety@continuity.net>,
Matt Smith <matt@nearapogee.com> and George <lists@southernohio.net>
on the mongrel-unicorn@rubyforge.org mailing list for their
feedback and testing for this release.