Add use_formal_grammar option to runtests.

runtests.py

@@ -1771,6 +1771,7 @@ def main():
     parser.add_option("--watermark", dest="watermark", default=None,
                       help="deterministic generated by string")
     parser.add_option("--use_common_utility_dir", default=False, action="store_true")
+    parser.add_option("--use_formal_grammar", default=False, action="store_true")
 
     options, cmd_args = parser.parse_args()
 
@@ -1830,6 +1831,7 @@ def main():
         Options.generate_cleanup_code = 3   # complete cleanup code
         from Cython.Compiler import DebugFlags
         DebugFlags.debug_temp_code_comments = 1
+        pyrex_default_options['formal_grammar'] = options.use_formal_grammar
 
     if options.shard_count > 1 and options.shard_num == -1:
         import multiprocessing