Another kerberos patch

If a con <<krbhost.patch>> nection is attempted with kerberos 5
authentication without specifying a hostname (using hostaddr), libpq
will crash in the kerberos libraries. Incidentally, this is the kind of
connection string pgAdmin3 uses...
(There is a comment in fe-connect.c that says the hostname has to be set
if we want to use kerberos, but there is no check for it)

Error affects both win32 and unix. It may not always produce a crash,
but it's always incorrect.

Attach patch checks that hostname is specified.

Please apply to both 8.0.X and 8.1.

//Magnus