[wsgi] Fix unicode decoding in POST
The application/x-www-form-urlencoded sent by firefox or chrome is utf-8
encoded BEFORE being urlencoded.
Hence, decoding must urldecode THEN decode the utf-8 string, and not the
other way around.
missing-dep-for-interpreter make => make | build-essential | dpkg-dev (usr/share/pyshared/cubicweb/skeleton/debian/rules.tmpl)