Tone down canonical-name resolution when using getaddrinfo(). Previously

Tone down canonical-name resolution when using getaddrinfo(). Previously
we were doing a forward+reverse lookup, which seems above and beyond the
call of duty, especially given that getaddrinfo() can be persuaded to
return a canonical name (this is what unix/uxnet.c does).

Unfortunately, I'm unable to test this at all as Win98 doesn't have
getaddrinfo(); hopefully I'll be able to find a mug with a modern version
of Windows to check it's not completely broken.

I think the effects of this are mostly cosmetic -- the canonical name is
used for window titles (and some people have been annoyed at the new
behaviour), other displays, and probably also for proxy exclusions.

git-svn-id: svn://svn.tartarus.org/sgt/putty@5614 cda61777-01e9-0310-a592-d414129be87e