iface/gspn/dcswaveltl.test, iface/gspn/dcswaveeltl.test, iface/gspn/dcswavefm.test: Do not accept $? = 0 when a failure is expected.
(eltlgspn_srg_SOURCES, eltlgspn_srg_LDADD, eltlgspn_srg_CPPFLAGS): New variables. (TESTS): Add dcswaveeltl.test. * iface/gspn/dcswaveeltl.test: New file. * iface/gspn/ltlgspn.cc [CEC]: Use emptiness_check.