upgrade and fix vpnc on 10.9

VPNC was unusable on Mavericks: 
1) tpcdump showed that traffic would be sent to the cisco vpn concentrator, but incoming traffic would simply be discarded by vpnc.
2) DNS queries would always use my isp's DNS server, making internal DNS names (split horizon) unresolvable.

This PR upgrades vpnc to 0.5.3r512 (same version as used by debian 7), which fixes 1).
Also, the formula contains a patch to vpnc-script to make OSX use the VPN DNS server, which solves 2).

Unfortunately, I do not have time to run extensive tests and do not have any previous OSX systems to test this against, so please run your own tests before merging :)

EDIT: looks like 2) is not fixed, I got fooled by the fact that dig and host use /etc/resolv.conf whereas getaddrinfo() doesn't...