Update required system-tools-backends to 2.1/2.2

[Carlos Garnacho <carlosg gnome org>]

Hi!,

As seen on http://live.gnome.org/TwoPointSeventeen/ExternalDependencies
system-tools-backends minimum dependency version is 1.9.7, it would be
great to upgrade that dependency to 2.1.2, it features the extensible
list of supported interface configuration methods and wireless key types
(for example, Feisty has support for local Zeroconf networks, and the
g-s-t frontends should notice this without affecting other
distributions)

Another desirable effect is that the 2.1.x versions use a lightweight
dispatcher, reducing hugely memory consumption during inactivity
compared to the 1.9/2.0 versions (marvels of interpreted languages...)

Obviously, the plan is to release s-t-b 2.2.0 with/before gnome 2.18.
Opinions?

Regards,

	Carlos