The attached patch adds support to vncviewer to run with a '-Parent windowid'
option and then use that window as its parent instead of the main window.  It's
a little rough, but seems to work well enough for now so that I can embed the
VNC viewer in a pygtk app for accessing Xen guests.

Longer term, I'm unsure whether we'll want to continue to go with this approach
or if we'll want to write a widget using libvncclient.