The attached patch provides a new gnus-dbus.el library, allowing systems
with dbus support to register a signal that closes all Gnus servers when
the system is going down for sleep. This is kind of a stop-gap solution
for the larger problems discussed in #40748.

It only does anything if Emacs has been compiled with dbus support, and
if the user sets the `gnus-dbus-close-on-sleep' to non-nil (it defaults
to nil).

Right now I've done this by checking the value of that option in
`gnus-1', but I could just as easily have the library add a startup
hook.

I assume this would require a mention in the manual. Is it something
we'd add to NEWS, as well?

Thanks,
Eric