Bug#776532: live-build: binary stage lacks use of chroot_dpkg script

[jnqnfe <jnqnfe@gmail.com>]

Package: live-build
Version: 5.0~a2-1

The binary stage script is missing chroot_dpkg in the list of chroot
'prep' scripts that are executed against the chroot filesystem.

I'm not certain if it was deliberately left out or not (the remove entry
is indeed there), and use of syslinux as the selected bootloader seems
fine without it when simply executing 'lb build', however I've been
meaning to bring this up for a while and I just ran into a problem.
While investigating something else, I manually executed the chroot prep
scripts listed in the binary stage against a previously used chroot
directory (previously used for a live-build build), then executed the
following command (as per usage in the chroot function):

sudo chroot chroot /usr/bin/env -i HOME="/root"
PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin"
aptitude install isolinux syslinux-common

This resulted in the following warnings and errors:

-----------------------------
<usual aptitude download stuff>
debconf: unable to initialize frontend: Dialog
debconf: (TERM is not set, so the dialog frontend is not usable.)
debconf: falling back to frontend: Realine
dpkg: warning: 'start-stop-daemon' not found in PATH or not in executable
dpkg: error: 1 expected program not found in PATH or not executable
Note: root's PATH should usually contain /usr/local/sbin, /usr/sbin and
/sbin
E: Sub-process /usr/bin/dpkg returned an error code (2)
Failed to perform requested operation on package. Trying to recover:
dpkg: warning: 'start-stop-daemon' not found in PATH or not in executable
dpkg: error: 1 expected program not found in PATH or not executable
Note: root's PATH should usually contain /usr/local/sbin, /usr/sbin and
/sbin
-----------------------------

Executing "sudo lb chroot_dpkg install" and then repeating the command
solves the problem (though the debconf messages remain).

So I assume that chroot_dpkg indeed should be used.