various tests of flaming monsters

This change adds a new flaming() macro and uses it in several places
where the list of flaming monsters was tested.  on_fire() didn't list
salamanders as already being on fire, but should have.  A couple other
cases were not updated to include flaming sphere.

src/mondata.c

@@ -692,6 +692,7 @@ struct attack *mattk;
     case PM_FLAMING_SPHERE:
     case PM_FIRE_VORTEX:
     case PM_FIRE_ELEMENTAL:
+    case PM_SALAMANDER:
 	what = "already on fire";
 	break;
     case PM_WATER_ELEMENTAL: