Bug fixes - Out for vengence.

See commit messages.

Fixes #5447
Fixes #5574
Fixes #5444
Fixes #5287
Fixes #5518
Fixes #5728
This snuck in (change is ghosts won't hear the vox screaching all the time just because they heard them on another z level).  If you want I can remove it, it's something that annoyed me along with hearing experiment 97B giggling half the time.