UDisks dbus async calls don't work sometimes when a second mainloop exists

[Havoc Pennington]

You may need to use the idle handler, but keep track of whether
anything happens before the idle handler runs that would affect that
handler...

A possibly-helpful thing is to use g_idle_add_full() to add an "idle"
at default or even high priority. Then the "idle" will be scheduled
round-robin with other events, or if higher priority, before other
events. Depends on the details whether this would eliminate races or
just make them less likely.

Havoc