Add NetBSD keyword.

Revert r1.4.
The changes are minimal and they cause redraw problems (as reported by
Maxim Devaev on port-sparc).

Add some acceleration using the P9100 quad and blit commands:
- for solid fill (quad)
- for pixmap copy (blit) when source and destination pitch are the same

Don't nest comments.

Don't define MaxClip and junk twice, fixing build with -fno-common.

Add support for EXA, so that the pnozz driver works again with Xorg.
Note, that only minimal acceleration is currently supported.

Thanks to macallan for the pointers to get this working.