loading_old_minetest_worlds.txt

If the world does not have a world.mt file with "gameid = minetest" or "gameid = mesetint" line in it, add it.

If the world is from earlier than something like 2011-05, apply the following patch, which appears to be needed for such worlds.

diff --git a/src/content_mapnode.cpp b/src/content_mapnode.cpp
index a6bf0a8..496f6b8 100644
--- a/src/content_mapnode.cpp
+++ b/src/content_mapnode.cpp
@@ -161,7 +161,13 @@ void content_mapnode_get_name_id_mapping(NameIdMapping *nimap)
        nimap->set(0x817, "default:nyancat");
        nimap->set(0x818, "default:nyancat_rainbow");
        nimap->set(0x819, "default:apple");
-       nimap->set(0x820, "default:sapling");
+       // Should be "default:sapling" but for some reason all air has this ID in
+       // many old worlds
+       nimap->set(0x820, "air"); // WTF?
+       // No idea what is going on with this but apparently old worlds (like
+       // version 13 or something) contain this id in places that should obviously
+       // be air
+       nimap->set(0xfe0, "air"); // WTF?
        // Static types
        nimap->set(CONTENT_IGNORE, "ignore");
        nimap->set(CONTENT_AIR, "air");