- Added a RETI instruction for returning 15-bit signed immediate values.

- Changed Actor's Damage property into an actual function. All access to the damage property
  must now be done through GetMissileDamage. actor->GetMissileDamage(0, 1) is equivalent
  to the former actor->Damage, for the case where actor->Damage was not an expression. (I
  suppose I will probably need to make a thunk for DECORATE expressions that want to read it.)
- Cleaned up some decorate expression evaluation functions that are no longer used.

SVN r3919 (scripting)

src/g_doom/a_bossbrain.cpp

@@ -47,7 +47,7 @@ static void BrainishExplosion (fixed_t x, fixed_t y, fixed_t z)
 				boom->SetState (state);
 		}
 		boom->effects = 0;
-		boom->Damage = 0;	// disables collision detection which is not wanted here
+		boom->Damage = NULL;	// disables collision detection which is not wanted here
 		boom->tics -= pr_brainscream() & 7;
 		if (boom->tics < 1)
 			boom->tics = 1;