The policy kit and HAL node device drivers both require a

DBus connection. The HAL device code further requires that
the DBus connection is integrated with the event loop and
provides such glue logic itself.

The forthcoming FirewallD integration also requires a
dbus connection with event loop integration. Thus we need
to pull the current event loop glue out of the HAL driver.

Thus we create src/util/virdbus.{c,h} files. This contains
just one method virDBusGetSystemBus() which obtains a handle
to the single shared system bus instance, with event glue
automagically setup.

include/libvirt/virterror.h

@@ -87,6 +87,7 @@ typedef enum {
     VIR_FROM_CAPABILITIES = 44, /* Error from capabilities */
     VIR_FROM_URI = 45,          /* Error from URI handling */
     VIR_FROM_AUTH = 46,         /* Error from auth handling */
+    VIR_FROM_DBUS = 47,         /* Error from DBus */
 } virErrorDomain;