- Added support for THRU flags on bullets and rails.

- ALLOWTHRUFLAGS must be used on the puffs, added for the sake of compatibility with older mods. This applies to the following:
-- Bullets: THRUACTORS, THRUSPECIES
-- Rails: Same as bullets, but includes THRUGHOST.

src/thingdef/thingdef_data.cpp

@@ -256,6 +256,7 @@ static FFlagDef ActorFlagDefs[]=
 	DEFINE_FLAG(MF7, FORCEDECAL, AActor, flags7),
 	DEFINE_FLAG(MF7, LAXTELEFRAGDMG, AActor, flags7),
 	DEFINE_FLAG(MF7, ICESHATTER, AActor, flags7),
+	DEFINE_FLAG(MF7, ALLOWTHRUFLAGS, AActor, flags7),
 
 	// Effect flags
 	DEFINE_FLAG(FX, VISIBILITYPULSE, AActor, effects),