Bug#1127550: debsums: dpkgdir option to use apt backups + md5sum option documentation improvement

[Ian Reynolds]

Package: debsums
Version: 3.0.2.3
Severity: normal
X-Debbugs-Cc: opsbugs at bluink.ca

When trying to find the right combination of rootdir and admindir for our backup
verification systems, it became clear that the DPKG variable being formed from
two variables creates confusion and can lead to errors. The attached patch file 
adds a very simple and direct way to tell debsums where to look for the dpkg
tree. The new -D option allows us to use our backed up dpkg --get-selections
output in a separate root for static VMs/containers.

Also - while the -m option would appear to allow you to verify an installed
package against a single md5sums file, this is not the case. The added line of
usage is an attempt to make the actual use of this flag clearer.


-- System Information:
Debian Release: 13.3
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable-security'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 6.12.63+deb13-amd64 (SMP w/12 CPU threads; PREEMPT)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages debsums depends on:
ii  libdpkg-perl          1.22.21
ii  libfile-fnmatch-perl  0.02-3+b4
ii  perl                  5.40.1-6

debsums recommends no packages.

Versions of packages debsums suggests:
ii  bash-completion  1:2.16.0-7

-- no debconf information