first merge of netbsd changes. not tested yet.

fixes for CVE CVE-2013-6424:

If t->bottom is close to MIN_INT, removing top can wraparound, so do the check properly.

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

initial import of xorg-server-1.6.1.901

initial import of xorg-server-1.4.2