pre_distupgrade_debug_packagemanager: enable Debug::pkgPackageManager

Signed-off-by: Andreas Beckmann <anbe@debian.org>
lib/db: simplify _find_packages_ready_for_testing()

Signed-off-by: Andreas Beckmann <anbe@debian.org>
lib/db: remove reserved packages from candidates

avoid rrdeps computation if not needed
avoid O(n^2) looping over previously reserved packages

Signed-off-by: Andreas Beckmann <anbe@debian.org>
make tmpdir setting mandatory for master/slave operation

use /var/cache/piuparts/tmp for the piuparts-slave package

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p.conf: add [global] PYTHONPATH setting

for non-default installations that use piuparts from git
in some other location than /usr

Signed-off-by: Andreas Beckmann <anbe@debian.org>
master-bin/slave-bin: get PYTHONPATH from piuparts.conf

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p.conf: get rid of [global] prefix setting

obsoleted by PYTHONPATH setting and @sharedir@ substitution

Signed-off-by: Andreas Beckmann <anbe@debian.org>
new known problem: should be rebuilt with newer tools

packages producing warnings from e.g. install-info or tex-common

Signed-off-by: Andreas Beckmann <anbe@debian.org>