basement & barn construction fix:  map::is_indoor uses the indoors or supports_roof t_flags

instead of checking if surrounding tiles are t_floor. This (partially) fixes
furnitures in basements and barns, and fixes opening and closing
windows in barns. Note that smashing/deconstructing furniture will
still generate t_floor tiles, instead of t_rockfloor, t_dirtfloor,
or whatever.