SF patch 536615: travel cache

This is derived from the proposed patch and feedback to it.  This applies
the last-position cache behavior without an option, making the behavior
more like it is for interfaces with a mouse, where holding the mouse still
acts the same way as the travel cache.  The code is not #ifdef'd either.

src/hack.c

@@ -768,6 +768,7 @@ boolean guess;
 				    nomul(0);
 				    /* reset run so domove run checks work */
 				    flags.run = 8;
+				    iflags.travelcc.x = iflags.travelcc.y = -1;
 				}
 				return TRUE;
 			    }