piuparts.conf.anbe: [global] and [DEFAULT] settings

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p.conf.anbe: [sid] (--warn-on-leftovers-after-purge)

* default settings: --warn-on-leftovers-after-purge
* for a better coverage
* retest monthly
* rebuild basetgz every two days

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p.conf.anbe: [jessie]

* rebuild basetgz weekly

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p.conf.anbe: [wheezy]

* --warn-on-debsums-errors in wheezy
* rebuild basetgz monthly

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p.conf.anbe: [squeeze]

* --warn-on-debsums-errors in squeeze
* ignore modification of /etc/shells: before wheezy a default list was
  shipped that may be modified if piuparts tests cause install/remove
  of shell packages that register and unregister a shell
* rebuild basetgz monthly

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p.conf.anbe: [experimental]

* retest monthly

Signed-off-by: Andreas Beckmann <anbe@debian.org>
remove empty entries from debian/changelog
shuffle+reword some TODO entries, remove 'confirm #660350' as is has been done
Use correct grammar in debian/changelog.
Add piuparts_slave_run.8 and piuparts_slave_join.8 manpages.
release as 0.52
start with 0.53

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