set defaults for known-problem-directory

don't set known-problem-directory in piuparts.conf, there is
not really a need to change this from the default currently

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p: disable using pdiffs

pdiffs cost a lot of cpu in order to save some bandwidth
that's useless with a local mirror or proxy

Signed-off-by: Andreas Beckmann <anbe@debian.org>
p-report: reintroduce <br> in menu about configuration
grammar
report: more bikeshedding, TODO is maintained in develop ;)
slave_run: allow starting of certain slaves
slave.conf: treat squeeze2wheezy with higher precedence
Makefile: support placeholder substitution in *-bin/*.py

Signed-off-by: Andreas Beckmann <anbe@debian.org>
dwke: add .py suffix to allow placeholder substitution

Signed-off-by: Andreas Beckmann <anbe@debian.org>
switch default Ubuntu distribution to "saucy".
debian/changelog: add Closes: for 678725
TODO: remove duplicate entry. also, sources.txt need to stay in htdocs
debian/changelog: re-order entries
release as 0.51