Replaces ex_act and emp_act numbers with defines

code/modules/events/immovable_rod.dm

@@ -80,7 +80,7 @@ In my current plan for it, 'solid' will be defined as anything with density == 1
 
 	if(isturf(clong) || isobj(clong))
 		if(clong.density)
-			clong.ex_act(2)
+			clong.ex_act(EXPLODE_HEAVY)
 
 	else if(isliving(clong))
 		penetrate(clong)
@@ -100,4 +100,4 @@ In my current plan for it, 'solid' will be defined as anything with density == 1
 		var/mob/living/carbon/human/H = L
 		H.adjustBruteLoss(160)
 	if(L && (L.density || prob(10)))
-		L.ex_act(2)
+		L.ex_act(EXPLODE_HEAVY)