MultiThreaded Demo:

- fixing various race conditions throughout (usage of static vars, etc)
 - addition of a few lightweight mutexes (which are compiled out by default)
 - slight code rearrangement in discreteDynamicsWorld to facilitate multithreading
 - PoolAllocator::allocate() can now be called when pool is full without
     crashing (null pointer returned)
 - PoolAllocator allocate and freeMemory, are OPTIONALLY threadsafe
     (default is un-threadsafe)
 - CollisionDispatcher no longer checks if the pool allocator is full
     before calling allocate(), instead it just calls allocate() and
     checks if the return is null -- this avoids a race condition
 - SequentialImpulseConstraintSolver OPTIONALLY uses different logic in
     getOrInitSolverBody() to avoid a race condition with kinematic bodies
 - addition of 2 classes which together allow simulation islands to be run
   in parallel:
    - btSimulationIslandManagerMt
    - btDiscreteDynamicsWorldMt
 - MultiThreadedDemo example in the example browser demonstrating use of
   OpenMP, Microsoft PPL, and Intel TBB
 - use multithreading for other demos
 - benchmark demo: add parallel raycasting

src/BulletCollision/BroadphaseCollision/btDbvtBroadphase.h

@@ -87,6 +87,7 @@ struct	btDbvtBroadphase : btBroadphaseInterface
 	bool					m_releasepaircache;			// Release pair cache on delete
 	bool					m_deferedcollide;			// Defere dynamic/static collision to collide call
 	bool					m_needcleanup;				// Need to run cleanup?
+    btAlignedObjectArray< btAlignedObjectArray<const btDbvtNode*> > m_rayTestStacks;
 #if DBVT_BP_PROFILE
 	btClock					m_clock;
 	struct	{