id_heads.h, wl_game.c, wl_play.c: changed mapwidth/mapheight to #defines,
since only maps with size 64x64 are allowed

vi_xlib.c, vi_svga.c, vi_null.c, vi_wdx.c, id_vh.c: moved VL_DeModeXize
to id_vh.c

vi_xlib.c: Part 2 of rewrite