Un-hard-code the random seed.
Room : update sky-groups _after_ doing borders -- to allow windows (etc) to
be placed and thereby force the sky to a certain minimum height.
More tidying in Render_edge(), renamed 'bord' --> 'info', and generally
don't pass parameters to the construnction functions.
Map borders : convert "scenic" areas which are not outdoor to "void".
Partial work to support "window" junctions.