The recent upgrade did not deal with obsolete conffiles properly.
Please use the dpkg-maintscript-helper support provided by dh_installdeb
to remove these obsolete conffiles on upgrade.

https://www.debian.org/doc/debian-policy/ch-files.html#s-config-files
http://manpages.debian.org/man/1/dh_installdeb

This bug report brought to you by adequate:

http://bonedaddy.net/pabs3/log/2013/02/23/inadequate-software/

$ pkg=ubuntu-dev-tools ; adequate $pkg ; dpkg-query -W -f='${Conffiles}\n' $pkg | grep obsolete
ubuntu-dev-tools: obsolete-conffile /etc/bash_completion.d/pbuilder-dist
 /etc/bash_completion.d/pbuilder-dist dcf466220e868c68cc6947906bc7a15b obsolete