Implement THREAD_PRIORITY_TIME_CRITICAL

[Mike Hearn]

>> More on topic, does this simply change Wine's priority or does it act on 
>> a per-thread level? Most of the issues I've seen have been caused by the 
>> audio thread being starved by the others, and is often semi-solved by 
>> running Wine at nice 19

The latter. I did try renicing Wine first, but no joy.

> BTW, I have to admit that I'm astonished that someone before stated that
> SCHED_ISO wasn't sufficient for his audio work. 

I am too, having seen the definition of SCHED_ISO, nonetheless that's 
what was reported. I haven't seen any other comments about using 
SCHED_ISO with audio apps except that one, so it gives me pause for concern.

And even then, SCHED_ISO is a long way off and may never be merged. 
Waiting for it wouldn't be helping users today, which is a bad thing IMHO.

thanks -mike