Unfortunately the change of /etc/udhcpc/libicd_network_ipv4.script by vpnc IS NEEDED! Without it you may have a problem of access to VPN DNS. vpnc add some stuff into /etc/udhcpc/libicd_network_ipv4.script which allows your access to VPN DNS. So, - uninstall and reinstall vpnc... and remember the problem for next release.