[change] Introduce XbmcThreads::InversePredicate as a helper for threading mechanisms...

[change] Introduce XbmcThreads::InversePredicate as a helper for threading mechanisms that deal with predicates.

This is a slight modification that makes the code more readable and provides for a general mechanism to use condition variables in a more straightforward manner. This currently effects CSharedSection and CApplication. With respect to the use of TightConditionVariable, they should be cleaner now.