Enhancements for Render composite request

[Barry Scott]

Matthias Hopf wrote:
>   
>> The worst case
>> would be to split the screen in two with left and right windows. If both 
>> the left and
>> right apps ask for a tear free render the frame rate will halve.
>>     
>
> Good point. Though I guess you *could* optimize for these cases.
> It would be one hell of a logic block, though.
>   
Of course if you can composite the screen this case never happens.

Then you need to ensure that when the compositor does its
tear free write other OpenGL and X11 apps do not stale until
the tear free write completes.

Barry