fix #H7708 - change in terrain not noticed

Jumping or teleporting while levitating in xorn form wouldn't toggle
blocking of levitation when moving from open spots to wall/stone and
unblocking of same when moving the opposite way.

This handles those cases but there are no doubt others.  The only
other one I checked was when failed #untrap moves hero onto trap.
That case works correctly--at least after this fix is in place.

Noticed while working on it:  change of terrain didn't always update
the status line.  When levitation became blocked, it still said Lev
and when unblocked, didn't say that.  Next status update got status
condition back in sync.

src/teleport.c

@@ -1,4 +1,4 @@
-/* NetHack 3.6	teleport.c	$NHDT-Date: 1523306912 2018/04/09 20:48:32 $  $NHDT-Branch: NetHack-3.6.0 $:$NHDT-Revision: 1.73 $ */
+/* NetHack 3.6	teleport.c	$NHDT-Date: 1544401270 2018/12/10 00:21:10 $  $NHDT-Branch: NetHack-3.6.2-beta01 $:$NHDT-Revision: 1.81 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) Robert Patrick Rankin, 2011. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -340,6 +340,11 @@ boolean allow_drag;
     vision_full_recalc = 1;
     nomul(0);
     vision_recalc(0); /* vision before effects */
+    /* if terrain type changes, levitation or flying might become blocked
+       or unblocked; might issue message, so do this after map+vision has
+       been updated for new location instead of right after u_on_newpos() */
+    if (levl[u.ux][u.uy].typ != levl[u.ux0][u.uy0].typ)
+        switch_terrain();
     if (telescroll) {
         /* when teleporting by scroll, we need to handle discovery
            now before getting feedback about any objects at our