Bug#631246: live-build: allow building from optical disc images

[Tshepang Lekhonkhobe <tshepang@gmail.com>]

Package: live-build
Version: 3.0~a21-1
Severity: normal

If I use a CD/DVD image as an APT source, I get:

E: Failed getting release signature file... Release.gpg

Can you add an option to ignore that file since it's not included in Debian iso images.

-- Package-specific info:

-- System Information:
Debian Release: wheezy/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (500, 'testing'), (500, 'stable'), (1, 'experimental')
Architecture: i386 (i686)

Kernel: Linux 2.6.39-2-686-pae (SMP w/2 CPU cores)
Locale: LANG=en_ZA.utf8, LC_CTYPE=en_ZA.utf8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages live-build depends on:
ii  debootstrap                   1.0.32     Bootstrap a basic Debian system

Versions of packages live-build recommends:
ii  cpio                          2.11-7     GNU cpio -- a program to manage ar
ii  gettext-base                  0.18.1.1-3 GNU Internationalization utilities
ii  gnu-fdisk                     1.2.4-3    Linux fdisk replacement based on l

Versions of packages live-build suggests:
ii  dosfstools                    3.0.9-1    utilities for making and checking 
ii  fakeroot                      1.16-1     tool for simulating superuser priv
ii  genisoimage                   9:1.1.11-1 Creates ISO-9660 CD-ROM filesystem
ii  memtest86+                    4.20-1     thorough real-mode memory tester
ii  mtools                        4.0.12-1   Tools for manipulating MSDOS files
pn  parted                        <none>     (no description available)
pn  squashfs-tools | mtd-tools    <none>     (no description available)
ii  sudo                          1.7.4p6-1  Provide limited super user privile
pn  syslinux | grub               <none>     (no description available)
pn  uuid-runtime                  <none>     (no description available)
pn  win32-loader                  <none>     (no description available)

-- no debconf information