fix #H2591 - sitting while swallowed (trunk only)

fix #H2591 - sitting while swallowed (trunk only)

     From a bug report, sitting while
swallowed gave "you are sitting on air," and the intended message "there are
no seats in here" was never reached.  Move the latter so that it works, and
add a new one when you try to sit while a grabber is holding on to you.

     Also add theft vs donning fixes entry which was left out two days ago.