Instead of calling dbus_connection_send_with_reply_and_block, we do:

 - Setup watch functions in order to get fds and poll events when a callback is
   triggered.

 - Call dbus_connection_send_with_reply() (that won't do anything because no
   mainloop). This will trigger watch callbacks.

 - In loop: call vlc_poll_i11e() with fds fetched from the watch callbacks.
   Call dbus_watch_handle() on the polled fds. This will do the I/O (non
   blocking).

 - Wait for reply from the pending call.