[winswitch] Enabling Shadowing mode

[J.L.M.]

I can't seem to get shadowing mode to work. From what I'm reading, if the
application is using xpra, then it should just be available, but I do not
see it in the menu. I can only send from one computer to the other. I'm
running CentOS 6.5 64 bit and Windows XP.

What I would really like is to just send one window of a multi-window
application, but if that is not supported, then shadowing is fine, where I
will minimize one window on one computer, and minimize the other window on
the other computer.