[rql2sql] added test that shows crash during sql generation
Original query in cubicweb-drh:
Any A,E,CV,group_concat(TN) GROUPBY A,E,CV WHERE A is Application, A for_person P, P has_studied_in E?, T? tags A, T name TN, A curriculum CV?
Corresponding bug in tracker: #628798
debian/tmp/usr/lib/PY_VERSION/site-packages/cubicweb/hercule.py usr/lib/PY_VERSION/site-packages/cubicweb