added hashtable based PairManager, thanks Pierre Terdiman and Erin Catto
improved friction in 'cachefriendly' solver
moved 'refreshcontactpoints' into collision detection, instead of solver
avoid linear search for contact manifolds, by storing an index
ignore margin for sphere shape (its entire radius is already margin)
avoid alignment checks in BVH serialization, they don't compile on 64-bit architectures
made 'bomb' box more heavy
This is good when having lots of re-used shapes with different sizes.
Convex shapes will need to derive from btConvexInternalShape (which is a subclass of btConvexShape). We could have renamed btConvexShape to 'btConvexShapeInterface' (can still do that later)
It leads to problems with certain compilers, when Bullet/src is located in a long pathname.
Keep include path starting with "LinearMath/, "BulletCollision/, or "BulletDynamics/
