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/IslandCave/scripts.inc

@@ -66,7 +66,7 @@ IslandCave_EventScript_238EEF:: @ 8238EEF
 	end
 
 IslandCave_EventScript_238F13:: @ 8238F13
-	msgbox gUnknown_0827304E, 4
+	msgbox gUnknown_0827304E, MSGBOX_DEFAULT
 	releaseall
 	end