Install a few packages from backports (needed by tails-persistence-setup).

config/chroot_apt/preferences

@@ -18,10 +18,18 @@ Package: iceweasel
 Pin: origin mozilla.debian.net
 Pin-Priority: 999
 
+Package: libglib-perl
+Pin: origin backports.debian.org
+Pin-Priority: 999
+
 Package: libgnupg-interface-perl
 Pin: origin backports.debian.org
 Pin-Priority: 999
 
+Package: libgtk2-perl
+Pin: origin backports.debian.org
+Pin-Priority: 999
+
 Package: libio-socket-ssl-perl
 Pin: origin backports.debian.org
 Pin-Priority: 999
@@ -38,6 +46,10 @@ Package: libregexp-common-perl
 Pin: release o=Debian,a=unstable
 Pin-Priority: 999
 
+Package: libunix-mknod-perl
+Pin: origin backports.debian.org
+Pin-Priority: 999
+
 Package: libvpx0
 Pin: release o=Debian,a=unstable
 Pin-Priority: 999