The idea behind this is to outright remove the relative position adding from the engine side and let it happen with A_OverlayOffset instead. Still more work to do.
There were two booleans that could be merged into the flag word.
This also fixes a bug with CHAN_NOSTOP not working for local sounds because it checked the wrong sound source for the playing sound.
- added Marisa Kirisame's CHAN_OVERLAP flag.
- exported S_IsActorPlayingSomething to ZScript.
The sound API change required deprecating A_PlaySound and S_Sound. There are now new variants S_StartSound and A_StartSound which have two distinct parameters for channel and flags.
There are two options here - one only disables the vertical thrust and the other goes back fully to the original non-z-aware code.
Both options are settable through MAPINFO.
For the compatibility presets, the normal ones only disable the vertical thrust, the strict ones force use of the old code entirely.
