Re-added Carlo's double_quote(...)'s for the Windows SSH binaries.

Where I'm using subprocess.Popen with shell=False, I'm now using
sshBinary.strip('"').  Quoting requirements are different
depending on whether shell=True or False, e.g. see:
http://stackoverflow.com/questions/804995/how-to-use-subprocess-when-multiple-arguments-contain-spaces

I see that Chris is starting to use my new classes and
methods in sshKeyDist, e.g. KeyModel.addKeyToAgent(...)
I recently added a new callback for an error I was seeing on
Windows: "Could not open a connection to your authentication agent."
(see CVLFAB-600), so I added the new callback into Chris's code.