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

doc/fixes35.0

@@ -61,6 +61,7 @@ sync default documentation of "null" option with the code
 tripping over a cockatrice corpse didn't petrify, even when not wearing boots
 do not call swamps on the Juiblex level "moat" when freezing
 keep score from wrapping around and becoming negative by capping it
+kicked objects do not slide when on the air or water levels
 
 
 Platform- and/or Interface-Specific Fixes

src/dokick.c

@@ -454,6 +454,9 @@ xchar x, y;
 	if (is_pool(x, y)) {
 	    /* you're in the water too; significantly reduce range */
 	    range = range / 3 + 1;	/* {1,2}=>1, {3,4,5}=>2, {6,7,8}=>3 */
+	} else if (Is_airlevel(&u.uz) || Is_waterlevel(&u.uz)) {
+	    /* you're in air, since is_pool did not match */
+	    range + rnd(3);
 	} else {
 	    if (is_ice(x, y)) range += rnd(3),  slide = TRUE;
 	    if (kickobj->greased) range += rnd(3),  slide = TRUE;