Restore Perl 5.10 support

On Perl < 5.14, we can use Socket::GetAddrInfo from CPAN to replace the
missing getaddrinfo functionality of Socket.

Socket::GetAddrInfo < 0.22 requires :newapi in the import list, but 0.22
forbids it and enables the new API by default.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>