Add a "closed" property on session
This will simplify check and allow nicer error thatn the current "no _tx_data"
attribute error.
#! /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