Fixed recently introduced issue: can't re-use stack as member variable (to reduce memory allocs) in btDbvt, due to recursion.
remove btGjkEpa.* from Makefile.am, Makefile and CMakeLists.txt
avoid division-by-zero in ODE boxbox contact reduction
Disable btSphereBoxCollisionAlgorithm, it is broken.
More fixes for btSimpleBroadphase
Moved quickstep to Extras/quickstep folder, so developers don't get confused which constraint solver is default.