Please test peer (socket ident) auth on *BSD

I've applied patches to fix Martin Pitt's report of peer auth failing on
FreeBSD-amd64 kernels.  I tested it with FreeBSD but do not have the
resources to check every other platform that uses the same code branch
in auth_peer.  The buildfarm will soon tell us if the patches fail to
compile anywhere, but since the buildfarm doesn't test that
authentication path, it's not going to be as obvious whether it works.

So, if you have a BSD-ish machine, please try HEAD and see if peer auth
(or "ident" auth in older branches) still works for you.  Extra points
if you find out it used to be broken on your machine.  (Hey Stefan, did
you ever try that on spoonbill?)
        regards, tom lane