[AD] Screen update API again

[Evert Glebbeek <eglebbk@xxxxxxxxxx>]

A while back we discussed what we wanted to do with the screen update API 
in terms of it supporting things like triple buffering, double buffering 
etc. through a single interface.
I think concensus was that we wanted to go in the direction of the proposed 
Allegro 5 API, but I don't know how finalized this was. In the mean time, 
it may also be interesting to look at the code Chris Barry has written 
(although it doesn't look too different from the code that other Chris 
posted earlier):
http://www.allegro.cc/forums/view_thread.php?_id=397489&#target
with a few modifications, I think this could go into Allegro - if we don't 
have other plans for the gfx API.

Ideas? Comments?

Evert