Enable MPR by default

Add the contact point from MPR, in addition to SAT/clipping contacts. Added a new kernel to clear/reset the number of contacts in pairs (stored in the z component)
Always sample unit sphere directions, if there are more edge-edge combinations than unit sphere directions (162 by default)
Remember last running demo for Bullet 3 (and save it in a text file, Bullet
Enable the testFileFracture.bullet in the Bullet2FileDemo

src/Bullet3OpenCL/RigidBody/kernels/updateAabbsKernel.cl

@@ -11,3 +11,12 @@ __kernel void initializeGpuAabbsFull(  const int numNodes, __global b3RigidBodyD
 		b3ComputeWorldAabb(nodeID, gBodies, collidables, plocalShapeAABB,pAABB);
 	}
 }
+
+__kernel void clearOverlappingPairsKernel(  __global int4* pairs, int numPairs)
+{
+	int pairId = get_global_id(0);
+	if( pairId< numPairs )
+	{
+		pairs[pairId].z = 0xffffffff;
+	}
+}