spearmint: Have CGame pass sizes for various structs

Handle mismatched sizes. This allows extending the structs
without breaking backward/forward compatibility. Missing
fields are cleared.
spearmint: Remove glconfig_t run-time check

Extending glconfig_t doesn't break the API anymore, cgame says how big it is.
spearmint: Moved SAY defines from q_shared.h to mint-arena
Merge branch 'master' into sdl2