Allow the ForkLiftDemo to toggle between MLCP and SI solver, using F6 key.

Apply patch for CMake config, see Issue 754 (Issue 753)
Fix a few issue with the MLCP solver: allow split impulse, and fix offset in friction dependencies

src/BulletDynamics/ConstraintSolver/btSequentialImpulseConstraintSolver.h

@@ -134,6 +134,11 @@ public:
 		return m_btSeed2;
 	}
 
+	
+	virtual btConstraintSolverType	getSolverType() const
+	{
+		return BT_SEQUENTIAL_IMPULSE_SOLVER;
+	}
 };