[CF-Devel] Changes to random map code

[Peter Mardahl]

Hello,

1)  Treasure chests will no longer be dropped under walls, 
which was the cause of the 'trap in wall' problem Preston Crow noted.

2)  Monsters and chests won't appear on exits anymore.

3)  Keyplacement code is improved.  I fixed this case, which
could fail:

  ######D######
        #
        #

As far as I could tell, the two "no key" cases that Preston showed
me should have worked even with the old code.

PeterM