+ make compound versus soft body work (soft body uses interpolated transform)

+ fixed issue with persistent manifold, warmstarting values were not initialized properly
+ don't clear manifold in sphere-sphere collision (need warmstarting)
+ added support for 'split impulse', decouple positional error correction from velocity correction
This avoids adding momentum due to penetration correction, it can be tuned using following variables:
solverInfo.m_splitImpulse = true/false (disable/enable)
solverInfo.m_splitImpulsePenetrationThreshold (below this value, baumgarte/mixed velocity/penetration is used (cheaper, looks more plausible)
solverInfo.m_linearSlop (less jitter, when small amound of penetration is allowed)

src/BulletCollision/CollisionDispatch/btSphereSphereCollisionAlgorithm.cpp

@@ -56,7 +56,7 @@ void btSphereSphereCollisionAlgorithm::processCollision (btCollisionObject* col0
 	btScalar radius0 = sphere0->getRadius();
 	btScalar radius1 = sphere1->getRadius();
 
-	m_manifoldPtr->clearManifold();
+	//m_manifoldPtr->clearManifold(); //don't do this, it disables warmstarting
 
 	///iff distance positive, don't generate a new contact
 	if ( len > (radius0+radius1))