#ride workaround

#ride workaround

From the newsgroup:
> Apparent bug or weird-seeming feature:
> If you try to mount a horse that is already in a pit,
> you get the message "You lead the poor <foo> into a pit!"

     I checked into fixing this properly (you mount the steed and
then shared its trapped status without actively retriggering the
trap in the process), but the trap code is too convoluted to do
that cleanly.  So this "fix" just makes mounting attempts fail if
the steed is trapped.

     (This diff is mostly whitespace cleanup.)