shrink TODO
piuparts-slave.postrm: on purge, remove /var/cache/piuparts/tmp too.
update TODO

update TODO and add some comments to Makefile after reviewing
master+slave packages.
TODO: update plans for master-slave packages: no debconf usage, instead documentation.
TODO: the master-plan is not out-of-the-box anymore
p.conf.pejacevic: re-enable debsums failures

debsums from wheezy is sufficient

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