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[Maarten Maathuis]

These patches split off some exa code into more readable seperate files. And a 3rd implementation is added, which brings trapezoids 
back to reasonable performance for me (=nouveau driver pixmaps). It's completely transparent for the driver, all they have to do is 
set the flag. On the long term (post xorg 7.5) i have plans to do something more elaborate, but there is no way i will have that done 
in time for xorg 7.5 and we hope to switch to driver pixmaps as soon as possible.