DBus reconnect support (initial attempt)

[Havoc Pennington]

Hi,

fwiw I basically agree with Colin's post, that I don't think apps will
reliably handle a dbus restart correctly.

I *strongly* agree with Colin's post for the session dbus. It's crazy to
consider restarting that thing.

For the system dbus, I can imagine that the number of apps involved is
small enough that we might adapt most of them to handle the restart...
but I'm not optimistic.

So apps are welcome to try handling it, but I just would not expect it
to ever actually work reliably on real life systems.

Because we'll hold the protocol compatible post-1.0, a restart should
only be required for security updates.

Havoc