adds constants, cleans up callstd and msgbox code

* adds some constants for standard script names and messagebox types
* replaces some callstd calls with msgbox calls where equivalent
* replaces msgbox and callstd calls using raw digits with versions that use the constants

data/maps/SouthernIsland_Interior/scripts.inc

@@ -113,7 +113,7 @@ SouthernIsland_Interior_EventScript_242B8F:: @ 8242B8F
 	end
 
 SouthernIsland_Interior_EventScript_242B9A:: @ 8242B9A
-	msgbox SouthernIsland_Interior_Text_2A6AA1, 4
+	msgbox SouthernIsland_Interior_Text_2A6AA1, MSGBOX_DEFAULT
 	releaseall
 	end