linkeList: turn the bug printouts to debug level

We don't take any action anyway so no need to confuse users.
Remove all other log handlers when capturing logs

This avoids spurious error messages during test runs.
Document changes and release 0.6.16
Make sure we fixup the changelog trailer with newer devscripts

We don't change any mainttrailer options if already given.

Thanks: James McCoy for the detailed explanation
Closes: #740566
Brown paper bag, please

Gbp-Dch: Ignore
Use better variable name

It's a boolean indicating wether we fetch the author information from
git not the author information itself.

Git-Dch: Ignore
dch: Only modify the mainttrailer when --git-author is in use
buildpackage: Make debian-tag message configurable

New config option --git-debian-tag-msg allows for the specification of
the message format string for signed debian-tags.

When left unset, the default debian-tag-msg format is still:

    %(pkg)s Debian release %(version)s

Signed-off-by: Kamal Mostafa <kamal@whence.com>
Improve error messages on formatting errors

Make it easier for the user to detect misformated replacement strings in
config files and command line options.
gbp: add --version option

Closes: #758909
Allow to list all available commands
Unify doc strings a bit

since they now show up with --list-cmds
bash completion: make command list dynamic

Use "gbp --list-cmds" so we don't have to hardcode the available
commands and get support for the RPM ones as they show up.
Document changes and release 0.6.17
Don't delete *_source.changes on source only builds

Closes: #758726
Mention --no-merge

Closes: #760091
Document changes and release 0.6.18
Update to git-pbuilder 1.33
Document changes and release 0.6.19
Allow to always drop pq branch after export

Closes: #761160