Enable graphical benchmark by default in cmake

Toggle between point to point and generic 6dof constraint for mouse picking in the demos

Use a 'equal vertex thresdhold' in the btVoronoiSimplexSolver of  0.0001f by default.
This can be disabled (or configured) using defaultCollisionConfiguration->getSimplexSolver()->setEqualVertexThreshold(0.f);
See http://code.google.com/p/bullet/issues/detail?id=305

src/BulletCollision/CollisionDispatch/btDefaultCollisionConfiguration.h

@@ -112,6 +112,11 @@ public:
 		return m_stackAlloc;
 	}
 
+	virtual	btVoronoiSimplexSolver*	getSimplexSolver()
+	{
+		return m_simplexSolver;
+	}
+
 
 	virtual btCollisionAlgorithmCreateFunc* getCollisionAlgorithmCreateFunc(int proxyType0,int proxyType1);