Improvements, including compatibility issue.

We now save mount namespace info in a temporary directory. If you
upgrade from here, cleanup old directory with rm -rf
/root/mount_namespaces.

We add a show command for debugging, and fixup some minor bugs in
stop. Adds a check for silent failure of adding default route failure
which I might be the cause of an intermittent issue I've seen. I will
have to wait and see if it gets detected.