[py3] Decode subprocess stdout in toolsutils.show_diffs() On Python 3, subprocess' pipes are bytes stream so we must decode them before printing. Without this change, diff of configuration files (e.g. all-in-one.conf as displayed upon instance upgrade) will rendered as a single line on Python 3.

version=3
opts=uversionmangle=s/(rc|a|b|c)/~$1/ \
https://pypi.debian.net/cubicweb/cubicweb-(.+)\.(?:zip|tgz|tbz|txz|(?:tar\.(?:gz|bz2|xz)))