Install Florence from wheezy-backports, again (Closes: #5947).

Actually, the hide_on_start setting was simply migrated to dconf, under
a different name.

config/chroot_apt/preferences

@@ -15,6 +15,10 @@ Package: b43-fwcutter
 Pin: release o=Debian,a=unstable
 Pin-Priority: 999
 
+Package: florence
+Pin: origin backports.debian.org
+Pin-Priority: 999
+
 Package: poedit
 Pin: release o=Debian,a=unstable
 Pin-Priority: 1010