Remove momentum reduction in CA_JUMPTHOK

Also add new multiability handling for it

    This makes positional audio in sdl work correctly (things to the left
    play sounds in the left speaker)

This makes positional audio in sdl work correctly (things to the left
play sounds in the left speaker)

SDL1.2 is dead, long live SDL

to avoid a crash

Should now ignore all motion events and not warp the mouse when the
window is out of focus.

Fixes Furyhunter/SRB2#1 but probably makes mouse speed too slow on
Linux. Whatever.