add dummy 'ping' method

You cannot send an fd over dbus before authentication, but
authentication doesn't happen until you send a message.
So define a dummy 'ping' method which the standalone scm
programs can use to force authentication to happen, and
make movepid.c use it.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
chowncgroup and getpidcgroup: update to use dummy ping fn

And remove now-useless setting of SO_PEERCREED on the dbus socket
fd.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
unref the dummy message we sent

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
test10: cant use movepid.c unprivileged, use dbus-send

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
update proxy stubs to reflect new api

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>