polymorphing into a flyer while in a pit

<Someone> reported that if you polymorph into a flying monster while in a
pit, you must take u.utrap turns to first climb out before you can fly.  Of
course, once you're out, you can swoop down into the pit to pick things up
w/o delay.  Rather that have you automatically fly out (e.g. like quaffing
a potion of levitation), I thought it was better to take a turn to fly out,
so that's what I've implemented.

The code to deal with exiting a pit is moved to a new climb_pit function
and the "up" command now lets you climb from a pit too (something I've
found non-intuitive in the past).

Finally, I noticed that non-moving monsters could still go up/down even
though they couldn't move around.  Added non-moving checks in doup/dodown.

src/hack.c

@@ -1171,38 +1171,7 @@ domove()
 	}
 	if(u.utrap) {
 		if(u.utraptype == TT_PIT) {
-		    if (Passes_walls) {
-			/* marked as trapped so they can pick things up */
-			You("ascend from the pit.");
-			u.utrap = 0;
-			fill_pit(u.ux, u.uy);
-			vision_full_recalc = 1;	/* vision limits change */
-		    } else if (!rn2(2) && sobj_at(BOULDER, u.ux, u.uy)) {
-			Your("%s gets stuck in a crevice.", body_part(LEG));
-			display_nhwindow(WIN_MESSAGE, FALSE);
-			clear_nhwindow(WIN_MESSAGE);
-			You("free your %s.", body_part(LEG));
-		    } else if (!(--u.utrap)) {
-			You("%s to the edge of the pit.",
-				(In_sokoban(&u.uz) && Levitation) ?
-				"struggle against the air currents and float" :
-#ifdef STEED
-				u.usteed ? "ride" :
-#endif
-				"crawl");
-			fill_pit(u.ux, u.uy);
-			vision_full_recalc = 1;	/* vision limits change */
-		    } else if (flags.verbose) {
-#ifdef STEED
-			if (u.usteed)
-			    Norep("%s is still in a pit.",
-				  upstart(y_monnam(u.usteed)));
-			else
-#endif
-			Norep( (Hallucination && !rn2(5)) ?
-				"You've fallen, and you can't get up." :
-				"You are still in a pit." );
-		    }
+		    climb_pit();
 		} else if (u.utraptype == TT_LAVA) {
 		    if(flags.verbose) {
 			predicament = "stuck in the lava";