Upstream: detect port absence in fastcgi_pass with IP literal.

Upstream: detect port absence in fastcgi_pass with IP literal.

If fastcgi_pass (or any look-alike that doesn't imply a default
port) is specified as an IP literal (as opposed to a hostname),
port absence was not detected at configuration time and could
result in EADDRNOTAVAIL at run time.

Fixed this in such a way that configs like

http {
    server {
        location / {
            fastcgi_pass 127.0.0.1;
        }
    }

    upstream 127.0.0.1 {
        server 10.0.0.1:12345;
    }
}

still work.  That is, port absence check is delayed until after
we make sure there's no explicit upstream with such a name.