starting vpn before openvpn process is killed results in haywire

If you hit the main window button "Turn OFF" followed very quickly by hitting the button "Turn ON" in rapid succession, the client freaks out as it tries and fails to start a new openvpn before the prior one was killed off.

(from redmine: created on 2013-09-20, closed on 2013-10-23, relates #4060 (closed))