The lovely libvirtd goes into crazy mode if it receives broadcasts that
it didn't subscribe to. With bus-proxyd, this might happen in 2 cases:
1) The kernel passes us an unmatched signal due to a false-positive
bloom-match.
2) We generate NameOwnerChanged/NameAcquired/NameLost locally even
though the peer didn't subscribe to it.
dbus-daemon is reliable in what signals it passes on. So make sure we
follow that style. Never ever send a signal to a local peer if it doesn't
match an installed filter of that peer.
This implements a shared policy cache with read-write locks. We no longer
parse the XML policy in each thread.
This will allow us to easily implement ReloadConfig().
