Get rid of btSolverBody and use btRigidBody directly. btSolverBody didn't improve performance after all, due to random-access

Tweak the BenchmarkDemo a bit: 

1) disable deactivation in graphical mode
2) add some settings that increase performance in the BenchmarkDemo2 (1000 stack) from 35ms to 15ms on this quad core (at the cost of a bit of quality)

src/BulletDynamics/ConstraintSolver/btContactConstraint.h

@@ -54,8 +54,6 @@ public:
 	///obsolete methods
 	virtual void	buildJacobian();
 
-	///obsolete methods
-	virtual	void	solveConstraintObsolete(btSolverBody& bodyA,btSolverBody& bodyB,btScalar	timeStep);
 
 };