p.conf: set PYTHONPATH when running piuparts from git

piuparts needs to use piupartslib to read distros.conf

setting PYTHONPATH is only needed for running piuparts from git

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

Signed-off-by: Andreas Beckmann <anbe@debian.org>
distros.conf: add target-release

e.g. backports and experimental should be used with
apt-get -t <target-release> ...

Signed-off-by: Andreas Beckmann <anbe@debian.org>
lib/conf: DistroConfig: add support for target-release

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p: call 'apt-get -t <target-release>' if needed

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p.conf: put flags-{start,end}-squeeze into the [DEFAULT] section

consolidate flags used several times

ConfigParser looks there by default

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p.conf: squeeze2bpo2wheezy for piatti

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p.conf: reactivate lenny2squeeze

but disable recycling

Signed-off-by: Andreas Beckmann <anbe@debian.org>
distros.conf: add alias for testing

Signed-off-by: Andreas Beckmann <anbe@debian.org>
report_newly_bugged_packages: get_config_value accepts empty defaults

Signed-off-by: Andreas Beckmann <anbe@debian.org>
Changelog and ToDo updates

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p-r: fix section caching

Signed-off-by: Andreas Beckmann <anbe@debian.org>
update timeline in TODO