test: Check for host availability of IPv6 support properly
test: Check for host availability of IPv6 support properly

Check if host supports IPv6 protocol, and if not, skip the IPv6-related
bits.  Also, make sure that server listens on IPv6 loopback properly:
'localhost' may not always resolve to ::1.  In fact, a properly
configured system would most likely have 'localhost6' instead.  In any
case, it's better to use the IP addresses directly.

python-postgres/fe,python-postgres/fe