Add APT pinning to ignore Squeeze -specific packages in our APT repository.

Either they are backports for Squeeze, or they fix bugs that don't
affect Wheezy.

config/chroot_apt/preferences

@@ -18,6 +18,56 @@ Package: xul-ext-torbutton
 Pin: release o=Debian,a=unstable
 Pin-Priority: 999
 
+Explanation: override deb.tails.boum.org's Squeeze -specific package.
+Package: barry-util
+Pin: release o=Debian,a=testing
+Pin-Priority: 1010
+
+Explanation: override deb.tails.boum.org's Squeeze -specific package.
+Package: gcc-4.6
+Pin: release o=Debian,a=testing
+Pin-Priority: 1010
+
+Explanation: override deb.tails.boum.org's Squeeze -specific package.
+Package: libbarry0
+Pin: release o=Debian,a=testing
+Pin-Priority: 1010
+
+Explanation: override deb.tails.boum.org's Squeeze -specific package.
+Package: libmetacity-private0
+Pin: release o=Debian,a=testing
+Pin-Priority: 1010
+
+Explanation: override deb.tails.boum.org's Squeeze -specific package.
+Package: metacity
+Pin: release o=Debian,a=testing
+Pin-Priority: 1010
+
+Explanation: override deb.tails.boum.org's Squeeze -specific package.
+Package: metacity-common
+Pin: release o=Debian,a=testing
+Pin-Priority: 1010
+
+Explanation: override deb.tails.boum.org's Squeeze -specific package.
+Package: msn-pecan
+Pin: release o=Debian,a=testing
+Pin-Priority: 1010
+
+Explanation: override deb.tails.boum.org's Squeeze -specific package.
+Package: plymouth
+Pin: release o=Debian,a=testing
+Pin-Priority: 1010
+
+Explanation: override deb.tails.boum.org's Squeeze -specific package.
+Package: virtualbox-*
+Pin: release o=Debian,a=testing
+Pin-Priority: 1010
+
+Explanation: override deb.tails.boum.org's Squeeze -specific package.
+Package: xul-ext-adblock-plus
+Pin: release o=Debian,a=testing
+Pin-Priority: 1010
+
 Explanation: Unwanted package that tasksel would pull since they have Priority: standard.
 Package: apt-listchanges
 Pin: release o=Debian