[wp] Test for unsupported step limit

src/plugins/wp/tests/wp_plugin/no_step_limit.conf

+[main]
+default_editor = "editor %f"
+magic = 14
+memlimit = 1000
+running_provers_max = 2
+timelimit = 5
+
+[prover]
+command = "alt-ergo -timelimit %t %f"
+driver = "alt_ergo_2_2_0"
+in_place = false
+interactive = false
+name = "no-steps"

src/plugins/wp/tests/wp_plugin/no_step_limit.i

+/* run.config
+  DONTRUN:
+*/
+/* run.config_qualif
+  CMD: WHY3CONFIG=@PTEST_DIR@/@PTEST_NAME@.conf @frama-c@
+  OPT: -wp -wp-prover no-steps -wp-steps 10 -wp-msg-key shell
+*/
+/*@
+  lemma truc: \false ;
+*/

src/plugins/wp/tests/wp_plugin/oracle_qualif/no_step_limit.res.oracle

+# frama-c -wp -wp-steps 10 [...]
+[kernel] Parsing tests/wp_plugin/no_step_limit.i (no preprocessing)
+[wp] Running WP plugin...
+[wp] 1 goal scheduled
+[wp] Warning: no-steps  does not support steps limit (ignored option)
+[wp] [no-steps] Goal typed_lemma_truc : Unsuccess
+[wp] Proved goals:    0 / 1
+  no-steps:        0  (unsuccess: 1)