[datafeed] also catch EnvironmentError when trying to load the cwclientlib config file means the config file has not been found, so fall back to the old implementation instead of crashing.

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