stuck_in_wall tweak

When divine aid granted temporary Passes_walls ability to stuck hero,
it was giving 4d4 turns (4..16, avg 10).  But the first warning that
it's timing out is given at 4 turns left so wouldn't be seen if the
random amount of time picked was the minimum.  Switch to 4d4+4 (8..20,
avg 14) so that the message at 4 turns left will always happen.

src/pray.c

@@ -421,7 +421,7 @@ int trouble;
                Without something like this, fix_all_troubles can get
                stuck in an infinite loop trying to fix STUCK_IN_WALL
                and repeatedly failing. */
-            set_itimeout(&HPasses_walls, (long) d(4, 4));
+            set_itimeout(&HPasses_walls, (long) (d(4, 4) + 4)); /* 8..20 */
             /* how else could you move between packed rocks or among
                lattice forming "solid" rock? */
             You_feel("much slimmer.");