Previously Vel would be reset only if the target was moving. This change
ensures that Vel is always reset, as seems to be the intent of the
oldvel parameter.
- 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.