New and corrected area override modes.
Created by: Ovnuniarchos
AREA_SPACE_OVERRIDE_REPLACE has been split into two constants:
- _COMBINE_REPLACE, which works like the current _REPLACE, adding its grav/fric, then stops processing areas.
- _REPLACE, which replaces grav/fric with its own values, then stops processing areas.
There also is a new space override mode:
- _REPLACE_COMBINE, which replaces grav/fric with its own values, but keeps processing areas.
This has been done for both 2D and 3D areas. Documentation is still being written.