If an NX session does not have an actor and it is still connected somewhere (this should not happen... but it does), we should wait a bit then force the nxagent to disconnect (send kill -1)

This was mentioned in #198 but it seems like it was overlooked.

NXAGENT - Version 3.5.0

Copyright (C) 2001, 2011 NoMachine.
See http://www.nomachine.com/ for more information.

Info: Agent running with pid '8227'.
Session: Starting session at 'Wed Oct  3 00:44:12 2012'.
Error: Aborting session with 'Unable to open display 'nx/nx,options=/home/me/.winswitch/server/sessions/72/nx_options.txt:72''.
Session: Aborting session at 'Wed Oct  3 00:44:12 2012'.
Session: Session aborted at 'Wed Oct  3 00:44:12 2012'.

Why is all that extra stuff being sent to NX for the display, instead of it just being ":72"?

winswitch:
  Installed: 0.12.16-4
  Candidate: 0.12.16-4
  Version table:
 *** 0.12.16-4 0
        500 http://winswitch.org/ precise/main i386 Packages
        100 /var/lib/dpkg/status

In file ​http://winswitch.org/dists/lenny/main/binary-i386/Packages, as well as in Packages for other Debian/Ubuntu? versions, xpra is mentioned as a dependency for winswitch, but its description is missing in the mentioned Packages. The package correctly resides in ​http://winswitch.org/dists/lenny/main/binary-i386/xpra-0.0.7.16.i386.deb and after downloading and installing with

dpkg --install xpra-0.0.7.16.i386.deb

the installation of winswitch from the repository succeedes.