Always segregate zones with solid walls -- prevents player seeing too much
of the level at any one time, and keeps monster battles more manageable.
Sky groups : do not spread across a zone boundary (as zones are now strictly
segregated).
Watery borders : sometimes merge a touching void area into the water room.
Better handling of corners where areas meet, via new Corner_init() and
Corner_lookup() functions.
Corner system : store the map coordinate (x, y) in each CORNER object.
Moved fencepost logic --> new Layout_handle_corners() function.
Corner system : populate the 'junctions' field of each CORNER object.
Experiment with building narrow pillars on indoor area changes.
tweak
Weird shape generator : increased T_BRANCH_PROB --> 77