merge xorg-server 1.20.3.

first merge of netbsd changes. not tested yet.

add list_append() macro that xf86-video-nouveau 1.0.11 wants.

Constify list_is_empty.

With apologies to whoever will merge a newer version. Fortunately,
this file is getting replaced wholesale.

import xorg-server 1.9.2. important changes since 1.6.5 include:

- built-in symbol visibility, default not export
- fixes for various crashes
- many fixes for XI2, EXA, dix, render, glx, xkb, EDID, randr, Xv,
resource handling, Xext, vfb, xfree86 / vga and composite support.
- fixes several memory leaks
- many many documentation updates
- record extension enabled
- no longer looks for XF86Config files