New glucose code

[Alan Hourihane]

Carrying on from Zack's original idea and code, I've released some new
code on the glucose-2 branch which goes all the way to allowing xorg
drivers to use the xgl acceleration paths.

It's a simple one line call to initialize glucose in the driver as I
mentioned in the commit message. It's...

glucoseScreenInit(pScreen);

So, initialization only need to change such as .....

if (!exa && !xaa)
    glucoseScreenInit(pScreen);
else if (!exa)
    driversXAAinit(...);
else
    driversEXAinit(...);

It also works with Mesa's software renderer too, but is obviously slow,
but useful as a testing harness.

There's still a few niggly issues such as server shutdown causes
failures, but I'm working on those. There are also some rendering
glitches depending on which 3D driver you use, but they could well be
problems in the respective 3D drivers. Usually good to test with Mesa by
disabling DRI to check this.

As I've said, all the new code is on the glucose-2 branch, but I'll be
working to stabilize it and hopefully merge to the trunk in the future.

If there's any comments, etc, post away, and feel free to bang on the
code.

Alan.