pfacing resets player velocity to 0

As this is a commonly used function, this can be used to avoid fall damage when run just before landing. Player velocity should be looked up before the location set, then set back to that immediately afterwards. In the meantime, this can be worked around by doing this in code, but this shouldn't be necessary. Untested, but likely works with set_ploc as well, though perhaps this is not a problem.

Discussion wanted, as this is a breaking change.