xdmcp: Allow timed/autologin on remote displays

This commit readds the  security/AllowRemoteAutoLogin key
(deprecated in >= 2.20) and so XDMCP setups can be configured to use
autologin and timedlogin.

https://bugzilla.gnome.org/show_bug.cgi?id=624958
session: Make sure to clear the worker proxy as well

If we leak this, then we open ourselves up for trouble when we have
active outgoing requests on a freed conversation, leading to crashes and
other fun things.

https://bugzilla.gnome.org/show_bug.cgi?id=727589
session: disconnect dbus connection "closed" handler when no longer needed

We temporarily maintain a reference to a dbus connection to the worker
process in a linked list, while we wait for the worker to register.  If
we need to close the connection before the worker registers, then we
drop the held reference by way of a "closed" signal handler on the
connection object.

Once the worker registers, we remove the connection from the linked
list, and transfer ownership of the connection to a state variable in
the now running conversation object.  When performing the reference
transfer, we neglect to the disconnect the "closed" handler.

This commit makes sure the handler gets disconnected appropriately, so
it doesn't get called inappropriately.

https://bugzilla.gnome.org/show_bug.cgi?id=727589
session: get rid of the worker_connection state variable in conversation object

The conversation object maintains a pointer to the worker connection and
to the worker proxy.  The proxy already keeps a reference on the worker
connection, so there's no need to keep an explicit reference on the
connection directly.

This commit drops this extra reference.

https://bugzilla.gnome.org/show_bug.cgi?id=727589
session: make sure worker manager interface is freed up

Right now we unref the worker manager interface in one function:

stop_conversation_now

We neglect to unref it in stop_conversation and, of course, it's
owned by the conversation object so it should get freed when the
conversation is freed.

This commit changes the stop functions to deactivate the interface
in stop, changes the free function to drop the reference to the interface.

https://bugzilla.gnome.org/show_bug.cgi?id=727589
session: factor out duplicated code

The top half of stop_conversation and stop_conversation_now is
and should remain identical.  This commit refactors that part of
each function into its own function.

https://bugzilla.gnome.org/show_bug.cgi?id=727589
Updated Oriya translation