[cwconfig] Fix exception handling when building the cube dependency graph
UnorderableGraph exceptions do not have a 'cycles' property. A simple
cast to str does the job.
#! /bin/sh -e#if [ "$1" = configure ]; then if which install-docs >/dev/null 2>&1; then install-docs -i /usr/share/doc-base/cubicweb-doc fifi#DEBHELPER#exit 0