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/CMakeLists.txt

@@ -33,6 +33,7 @@ SET(BulletCollision_SRCS
 	CollisionDispatch/btInternalEdgeUtility.h
 	CollisionDispatch/btManifoldResult.cpp
 	CollisionDispatch/btSimulationIslandManager.cpp
+	CollisionDispatch/btSimulationIslandManagerMt.cpp
 	CollisionDispatch/btSphereBoxCollisionAlgorithm.cpp
 	CollisionDispatch/btSphereSphereCollisionAlgorithm.cpp
 	CollisionDispatch/btSphereTriangleCollisionAlgorithm.cpp
@@ -140,6 +141,7 @@ SET(CollisionDispatch_HDRS
 	CollisionDispatch/btHashedSimplePairCache.h
 	CollisionDispatch/btManifoldResult.h
 	CollisionDispatch/btSimulationIslandManager.h
+	CollisionDispatch/btSimulationIslandManagerMt.h
 	CollisionDispatch/btSphereBoxCollisionAlgorithm.h
 	CollisionDispatch/btSphereSphereCollisionAlgorithm.h
 	CollisionDispatch/btSphereTriangleCollisionAlgorithm.h