Fix DNS lookups of IPv6 addresses in URLs of web external tables.
Fix DNS lookups of IPv6 addresses in URLs of web external tables.

The code to look up an IP address based on a domain name checked
'!hostname', but 'hostname' is a local array, so the condition was never
true. When compiling with -Waddress, GCC gave a warning about it:

cdbutil.c: In function ‘getDnsCachedAddress’:
cdbutil.c:1239:23: warning: the address of ‘hostinfo’ will always evaluate as ‘true’ [-Waddress]
   if (((!use_cache && !hostinfo) || (use_cache && e == NULL))
                       ^

You don't see this normally, because we set -Wno-address in configure.in,
but it sure looks wrong.

I haven't been able to find a test case where this would cause a
user-visible failure. I think you'd need a domain name that resolves to
something that's not an IPv4 address, and use that domain in an external
table's URL.

greenplum-db/gpdb,xinzweb/gpdb,ashwinstar/gpdb,50wu/gpdb,adam8157/gpdb,adam8157/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,adam8157/gpdb,adam8157/gpdb,lisakowen/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,lisakowen/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,xinzweb/gpdb,50wu/gpdb,greenplum-db/gpdb,xinzweb/gpdb,xinzweb/gpdb,lisakowen/gpdb,50wu/gpdb,jmcatamney/gpdb,lisakowen/gpdb,jmcatamney/gpdb,xinzweb/gpdb,50wu/gpdb,lisakowen/gpdb,xinzweb/gpdb,50wu/gpdb,lisakowen/gpdb,50wu/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,adam8157/gpdb,jmcatamney/gpdb,xinzweb/gpdb,xinzweb/gpdb,lisakowen/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,lisakowen/gpdb,50wu/gpdb,adam8157/gpdb,adam8157/gpdb,50wu/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,adam8157/gpdb,ashwinstar/gpdb