Simplify GJK. Still needs double precision for large differences of feature scales.

Extract faces directly from btConvexHullComputer (in initializePolyhedralFeatures), instead of reconstructing them, thanks to Josh Klint in #1654
PyBullet: use initializePolyhedralFeatures for convex hulls and boxes (to allow SAT)
PyBullet: expose setPhysicsEngineParameter(enableSAT=0 or 1) to enable Separating Axis Test based collision detection for convex vs convex/box and convex versus concave triangles (in a triangle mesh).

src/BulletCollision/CollisionShapes/btPolyhedralConvexShape.h

@@ -43,6 +43,9 @@ public:
 	///experimental/work-in-progress
 	virtual bool	initializePolyhedralFeatures(int shiftVerticesByMargin=0);
 
+	virtual void setPolyhedralFeatures(btConvexPolyhedron& polyhedron);
+	
+
 	const btConvexPolyhedron*	getConvexPolyhedron() const
 	{
 		return m_polyhedron;