dbus_shutdown runtime checks

[Havoc Pennington]

frederic heem wrote:
> Hi,
> This problem has been found 2 month ago but still need to be fixed
> https://bugs.freedesktop.org/show_bug.cgi?id=8376

btw, this is a good lesson in the value of a minimal, compilable test 
case. On the bug report, John was probably testing with the session bus, 
which did not cause the problem, so he thought it was fixed; and you 
were testing with a GLib-based app that introduced a lot of extra noise 
and wild goose chase.

With the minimal test case, I immediately reproduced the problem and 
found the bug in a few minutes.

Havoc