Fetch installers of b43 firmwares from Debian unstable.

We fetch our kernel from there, and we'd better be consistent.
Also fetch b43-fwcutter from unstable, needed by the installer packages.
To this matter, enable Debian unstable contrib section.

config/chroot_apt/preferences

+Package: b43-fwcutter
+Pin: release o=Debian,a=unstable
+Pin-Priority: 999
+
 Package: eatmydata
 Pin: origin backports.debian.org
 Pin-Priority: 999
@@ -62,6 +66,14 @@ Package: firmware-atheros
 Pin: release o=Debian,a=unstable
 Pin-Priority: 999
 
+Package: firmware-b43-installer
+Pin: release o=Debian,a=unstable
+Pin-Priority: 999
+
+Package: firmware-b43legacy-installer
+Pin: release o=Debian,a=unstable
+Pin-Priority: 999
+
 Package: firmware-brcm80211
 Pin: release o=Debian,a=unstable
 Pin-Priority: 999

config/chroot_sources/sid.chroot

-deb http://ftp.us.debian.org/debian/ unstable main non-free
+deb http://ftp.us.debian.org/debian/ unstable main contrib non-free