[AD] X patch update

[Chris <kcat@xxxxxxxxxx>]

This patch implements XLOCK for acquire_screen, as well as the previous 
primitives patch. Since X is allowed to buffer calls and send them to 
the server en-mass, it seemed like a good idea to try and hold a lock 
while the screen is being drawn on.. since to me, it seems Allegro's 
putpixel test is XLOCK-limited, not speed-limited. And indeed, after 
implementation some of Allegro's primitives tests (circlefill, 
ellipsefill, etc, which rely on putpixel) showed substantial 
improvement.. more than double performance (circlefill went from ~400 
per second to ~1000 per second). I wouldn't doubt that if X buffers the 
PutImage calls, we could see a marked improvement there, too.

However, there is a slight cost. When running the demo game, using the 
DIGMID driver, I noticed a bit of stuttering in the sound. I can only 
guess that this is caused by the lock being held on the screen for too 
long while the screen->xbuffer conversion takes place and interrupting 
the input+sound thread. However, if the sound was put into its own 
thread (or perhaps even the timer thread), that issue would be resolved.

I also tried to make the X11 driver create an XImage with the same depth 
as Allegro's screen, leaving X to deal with the color conversion (since 
if it's running on a seperate thread, it would leave the Allegro program 
alone while it's converting the image). However, after having to reboot 
my computer due to it, I don't think I'm going to try persuing this 
again anytime soon.

- Kitty Cat

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