collides isn't unknown on tiles

lib/Properties.hs

@@ -492,6 +492,7 @@ checkTileThing removeExits p@(Property name _value) = case name of
             (dependsOn . Link)
             (const $ forbid "accessing local html files is disallowed.")
       | otherwise ->
+        when (not removeExits || name `notElem` [ "collides", "name", "tilesetCopyright" ]) $ do
           warnUnknown p knownTileLayerProperites
     where
       requireProperty req = propertyRequiredBy req name