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/BulletDynamics/CMakeLists.txt

@@ -21,6 +21,7 @@ SET(BulletDynamics_SRCS
 	ConstraintSolver/btTypedConstraint.cpp
 	ConstraintSolver/btUniversalConstraint.cpp
 	Dynamics/btDiscreteDynamicsWorld.cpp
+	Dynamics/btDiscreteDynamicsWorldMt.cpp
 	Dynamics/btRigidBody.cpp
 	Dynamics/btSimpleDynamicsWorld.cpp
 #	Dynamics/Bullet-C-API.cpp
@@ -70,6 +71,7 @@ SET(ConstraintSolver_HDRS
 SET(Dynamics_HDRS
 	Dynamics/btActionInterface.h
 	Dynamics/btDiscreteDynamicsWorld.h
+	Dynamics/btDiscreteDynamicsWorldMt.h
 	Dynamics/btDynamicsWorld.h
 	Dynamics/btSimpleDynamicsWorld.h
 	Dynamics/btRigidBody.h