fix #H260 - escaping lava let you stay there indefinitely

<email deleted>, escaping from being stuck
by lava via jumping--or simply walking--got you out of the lava while being
at the same location.  You could then stay there for as long as you liked
without falling back in.  This makes a lava and water check on turns where
time passes but hero hasn't moved, performing a subset of spoteffects().
I think the water case only matters when using wizard mode to wish for a
pool or moat, which gets created at hero's feet without making him fall in
(unlike wishing for lava, where hero does immediately fall in).

src/hack.c

@@ -1,4 +1,4 @@
-/*	SCCS Id: @(#)hack.c	3.5	2007/02/10	*/
+/*	SCCS Id: @(#)hack.c	3.5	2007/03/12	*/
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /* NetHack may be freely redistributed.  See license for details. */
 
@@ -1741,6 +1741,27 @@ stillinwater:;
 	return;
 }
 
+/* called if hero stays in the same spot while time passes */
+void
+stayeffects()
+{
+    /* leave the trickier cases to spoteffects()... */
+    if (u.uinwater) {
+	if (!is_pool(u.ux, u.uy)) spoteffects(FALSE);
+    } else if ((is_pool(u.ux, u.uy) || is_lava(u.ux, u.uy)) &&
+	    !(u.ustuck || Levitation || Flying)) {
+#ifdef STEED
+	if (u.usteed)
+	    spoteffects(FALSE);
+	else
+#endif
+	  if (is_lava(u.ux, u.uy))
+	    (void)lava_effects();
+	else if (!Wwalking)
+	    (void)drown();
+    }
+}
+
 /* returns first matching monster */
 STATIC_OVL struct monst *
 monstinroom(mdat,roomno)