String changes in gnome-system-tools

[Carlos Garnacho <carlosg gnome org>]

Hi!,

Before the string freeze applies completely, I've modified some strings
in services-admin from gnome-system-tools.

Oh, and btw, there have been also some small strings modifications in
system-tools-backends (in order to fix bug #308685) so I've already send
a mail to the Translation Project.

	Regards