Don't attempt to canonicalize peer name in Kerberos/GSSAPI/SSPI auth

[elprans]

libpq does not canonicalize and neither should we, because:

1. it's likely the wrong thing to do and removes control from the user;
2. it introduces a blocking DNS lookup into an async path, which is not
   great.

[eltoder]

Unfortunately, this does not work:

gssapi.raw.misc.GSSError: Major (851968): Unspecified GSS failure. Minor code may provide more information, Minor (2529638919): Server not found in Kerberos database 

But we can make the code follow libpq more closely and remove the gethostbyname_ex call. I'll send a PR.

[eltoder]

#1167