Install barry from squeeze-backports.

This much improved new version is effectively maintained, and is nice enough to
avoid displaying dozens of spurious error messages at boot time.

Closes: todo/upgrade_barry_to_fix_error_messages_on_boot

config/chroot_apt/preferences

@@ -2,6 +2,14 @@ Package: b43-fwcutter
 Pin: release o=Debian,a=unstable
 Pin-Priority: 999
 
+Package: barry-util
+Pin: origin backports.debian.org
+Pin-Priority: 999
+
+Package: libbarry18
+Pin: origin backports.debian.org
+Pin-Priority: 999
+
 Package: crda
 Pin: origin backports.debian.org
 Pin-Priority: 999