TODO
unit: no need to export variables if we can avoid it
udev: extern on functions is pointless
dbus: let's make this const array static
bus: add C++ wrappers to public header files
bus: consider it an error if the first message we get on the bus is not a reply to HELLO
bus: properly set up bus connections with sd_bus_set_exec()
bus: enable SO_PASSCRED only if we are not connected to a bus
bus: if we recieve fds but fd passing is off, consider this an error
prioq: consider a NULL prioq empty
bus: implement server mode, and anonymous authentication
bus: add missing test-bus-server.c