--trace=muscles

* src/getargs.h, src/getargs.c (trace_muscle): New.
	(trace_types, trace_args): Support it.
	* src/output.c (output_skeleton): Use it.
(cherry picked from commit 5263bea9f7)

src/getargs.h

@@ -106,6 +106,7 @@ enum trace
     trace_time      = 1 << 8,  /**< Time consumption. */
     trace_skeleton  = 1 << 9,  /**< Skeleton postprocessing. */
     trace_m4        = 1 << 10, /**< M4 traces. */
+    trace_muscles   = 1 << 11, /**< M4 definitions of the muscles. */
     trace_all       = ~0       /**< All of the above.  */
   };
 /** What debug items bison displays during its run.  */