remove prescient travel command behavior

Addresses reports R718, R772.1, <Someone> P's extra move bug
- when there is a previously seen path or a straight path, always take it
- incorporate fix to ensure no extra "." turn at the end of traveling, but
 still avoid stepping into traps/pools, et al
- include a general "G"-command (and travel) fix to avoid stepping in
 known pools/lava while blind
- when there is no such path, "guess" at a path by finding an intermediate
 location that the hero couldsee that is closest to the actual goal, the
 intermediate goal is re-determined at each step
- when Blind, don't use couldsee for determining straight paths, just direction
- do not consider doors or most boulders obstacles for picking travel
 paths, test_move has a new mode to differentiate this case from the regular
 test case
- don't include known trap locations in the travel path, avoids unnecessary
 stops along the way, and usually doesn't affect the path length
- reformatted the code a bit so I could follow it

doc/Guidebook.mn

@@ -476,7 +476,10 @@ Prefix:  move until something interesting is found.
 .lp "G[yuhjklbn] or <CONTROL->[yuhjklbn]
 Prefix:  same as `g', but forking of corridors is not considered interesting.
 .lp _
-Travel to a map location via a shortest-path algorithm. Stops on most of 
+Travel to a map location via a shortest-path algorithm.  The shortest path
+is computed over map locations the hero knows about (e.g. seen or
+previously traversed).  If there is no known path, a guess is made instead.
+Stops on most of
 the same conditions as the `G' command, but without picking up
 objects, similar to the `M' command.  For ports with mouse 
 support, the command is also invoked when a mouse-click takes place on a