Close the socket for the external VNC handler when done

Ignore-this: c3ea54bc827e7e1b1a6e2854a46045a3

darcs-hash:20100212120139-b22ec-11fafa0676a1dfb25371ed3bfcaf1729b43549f4
Handle case where stream fails to start and vnc_socket is None

Ignore-this: 5f2f482af7bcc7ac93335dd07d90d3c6

darcs-hash:20100212124026-b22ec-5b4b17ddf237c7534a8f1affb21e18aea132e3de