displacer beast as food

Make eating a displacer beast corpse or a tin of displacer beast
meat confer temporary Displacement lasting 6d6 turns.

src/eat.c

@@ -1075,6 +1075,11 @@ int pm;
             polyself(0);
         }
         break;
+    case PM_DISPLACER_BEAST:
+        if (!Displaced) /* give a message (before setting the timeout) */
+            toggle_displacement((struct obj *) 0, 0L, TRUE);
+        incr_itimeout(&HDisplaced, d(6, 6));
+        break;
     case PM_DISENCHANTER:
         /* picks an intrinsic at random and removes it; there's
            no feedback if hero already lacks the chosen ability */