Build full A matrix and b vector for a MLCP solver interface, to explore Lemke, Dantzig, Newton and other MLCP solvers. The A matrix contains sparsity information.

Added a PGS solver that uses the sparsity of the A matrix, just for testing (the equivalent sequential impulse solver is much faster, not having to allocate the big matrices)

src/BulletDynamics/ConstraintSolver/btSolverConstraint.h

@@ -55,6 +55,7 @@ ATTRIBUTE_ALIGNED16 (struct)	btSolverConstraint
 	{
 		void*		m_originalContactPoint;
 		btScalar	m_unusedPadding4;
+		int			m_numRowsForNonContactConstraint;
 	};
 
 	int	m_overrideNumSolverIterations;