Replaces them with forward declarations of used types, or removes them entirely if they aren't used at all. This also replaces certain Common headers with less inclusive ones (in terms of definitions they pull in).
This makes the code cleaner and also leads to some user-visible changes:
The wx game properties will no longer let the user
select WAD languages that don't have any names.
The Qt game list will now display names using the languages
set in the configuration instead of always using
English for PAL GC games and Japanese for WADs.
If a WAD doesn't have a name in the user's preferred language,
English is now selected as a fallback before Japanese.
