Unfortunately, you are too optimistic on vpnc - original file /etc/udhcpc/libicd_network_ipv4.script had some code to fix DNS over VPN and just replacing it with new version destroys that code. To fix this you should uninstall vpnc and install it again. BTW, month ago I noted that there are two packages vpngui and vpn-gui. The last one (vpn-gui) was very buggy but vpngui work perfect. Just FYI.