Use SInt32 for AtomicCompareAndSwap32; more useful for counters.
Call atomic operations directly in NAtomicInt.
Added NThread::GetID and NThread::AreEqual.
Document that atomic operations insert a memory barrier.
Split locks into separate classes, improve NMutex performance on Mac OS X.
Fix NSpinLock assert, OSSpinLock is set to -1 when acquired.