cubicweb-vcsfile #2057810 More explicit error logging [validation pending]

I get a bunch of logs that say

2011-10-26 14:27:24 - (cubicweb.sources.hg) ERROR: 67457.url: <urlopen error [Errno -2] Name or service not known>

It would be nice to include the URL in the error message so as to diagnose the problem

prioritynormal
typeenhancement
done in1.13.0
load left0.000
closed by#221255e9e57e [log] write url in log message on pull/clone failure (closes #2057810)
patch[log] write url in log message on pull/clone failure (closes #2057810) [applied]