[multi-source] add test case for an encountered bug, fixed by adding state_of to dont_cross_relations. Added a note to remind me that something should be done to be smarter in handling this

#!/bin/sh -e
if [ "$1" = "purge" ] ; then
        update-rc.d cubicweb remove >/dev/null
fi
 
#DEBHELPER#
 
exit 0