Fix stuck travel for good

My fixes to the travel stuck oscillation did not fix all of them,
and I've even seen a 3-step loop - which my fixes cannot detect.
I guess there could be arbitrary-sized loops too.

To definitely fix this, keep track of all the map locations travel
has moved the hero through, and if it tries to go on a location already
used, stop travel and give the unsure -message.

src/allmain.c

@@ -466,8 +466,7 @@ moveloop_core(void)
         }
         if (g.context.mv) {
             if (g.multi < COLNO && !--g.multi)
-                g.context.travel = g.context.travel1 = g.context.mv =
-                    g.context.run = 0;
+                end_running(TRUE);
             domove();
         } else {
             --g.multi;