U897: kicking while in the air

U897: kicking while in the air
If you kick something while in the air (i.e. on the Air level or while
in a bubble on the water level), 1) greased objects were treated specially
and 2) messages were given about the object sliding.
- add checks for kicking in the air, and always increased distance a bit
(I didn't add any checks to deal with the transition from air to water or
visa versa)
- don't set the flag that causes the "slides" message in these cases either