Backport 47e01ac from parallelism: D-Bus doesn't seem to depend on a writeable file system.
Backport 2fc2626 from parallelism: Check if a service has started or stopped.

Conflicts:
	usr/lib/yarfi/ServiceThread.py
	usr/lib/yarfi/service.py
Backport 692decc from parallelism: Not importing itself.
Backport aa21ca1 from parallelism: If the service isn't started yet, there could be perhaps no self.process.
Backport 2136deb from parallelism: The check whether D-Bus is running must be in a seperate process.
Added two services and one target for networking.
Network needs a filesystem.

Well, mounting something to /run would be sufficient, I guess.
Added a service for filesystems.
Added services and targets to halt, reboot and poweroff.

All services should depend on "system" now. (Unless they want to be the only process.)
A few changes to the services.

 * correct mounting (I think so.)
    Mount all in /etc/fstab _and_ remount,rw /.
 * ifupdown doesn't depend on filesystem
 * filesystem depends on ifupdown (for network filesystems in /etc/fstab).
 * two more comments (Well, they are the same.)
Use poll() instead of returncode to not create zombies.
Filesystem doesn't depend on ifupdown. Ifupdown depends on filesystem.
Allow passing arguments via sys.argv.
The shell doesn't depend on dbus. The whole target depends on dbus.
Merge recent changes from "both".

Conflicts:
	etc/yarfi/services/dbus.py
	etc/yarfi/services/exec_init.py
	etc/yarfi/services/single.py