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/btConstraintSolver.h

@@ -28,6 +28,14 @@ class btIDebugDraw;
 class btStackAlloc;
 class	btDispatcher;
 /// btConstraintSolver provides solver interface
+
+
+enum btConstraintSolverType
+{
+	BT_SEQUENTIAL_IMPULSE_SOLVER=1,
+	BT_MLCP_SOLVER=2
+};
+
 class btConstraintSolver
 {
 
@@ -44,6 +52,10 @@ public:
 
 	///clear internal cached data and reset random seed
 	virtual	void	reset() = 0;
+
+	virtual btConstraintSolverType	getSolverType() const=0;
+
+
 };
 
 

src/BulletDynamics/ConstraintSolver/btSequentialImpulseConstraintSolver.h

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