support compound versus compound collision shape acceleration on GPU, using aabb tree versus aabb tree.

Remove constructor from b3Vector3,  to make it a POD type, so it can go into a union (and more compatible with OpenCL float4)
Use b3MakeVector3 instead of constructor
Share some code between C++ and GPU in a shared file: see b3TransformAabb2 in src/Bullet3Collision/BroadPhaseCollision/shared/b3Aabb.h
Improve PairBench a bit, show timings and #overlapping pairs.
Increase shadowmap default size to 8192x8192 (hope the GPU supports it)

src/Bullet3Common/premake4.lua

@@ -5,6 +5,8 @@
 	kind "StaticLib"
 		
 	targetdir "../../bin"
+	
+	includedirs {".."}
 
 	files {
 		"**.cpp",