Patch: wake up duchainlock writers

[David Nolden]

Ok I've tried out the patch a bit, and this patch indeed makes the multi-cpu 
usage better. It somewhat reduces the 'elapsed time' of parsing a project. 
However it also increases the 'user time', which means that all in all, the 
effort is higher. I cannot tell exactly what the reason of this is, but 
probably QWaitCondition is just less efficient than a waiting loop.

Due to the central nature of the duchain lock, I'm actually thinking of 
replacing all the mutexes in there with spin-locks, using QAtomicInt instead 
of all the mutexes and wait conditions, to make the whole thing more 
efficient.

Greetings, David