Sph: various OpenCL optimizations, remove auto-sized workgroups.

-Swap rearranged array, instead of copying back(~3ms faster)
-Simultaneous CPU/GPU processing(~3ms faster)
-Remove max neighbor limit(~1ms faster)
-Remove '(i == n)' branch(~0.5-0.7ms faster)

Timings for 'Demo_ManyParticles' with 65536 particles on Radeon 5850,
btFluidSphSolverOpenCL::updateGridAndCalculateSphForces():
	~29ms -> ~22ms (after enabling GPU grid update)
	~22ms -> ~14ms (after various optimizations)

	~29ms -> ~25ms (after optimizations without GPU grid update)

	--Default configuration has GPU grid update disabled
Sph: fix OpenCL AABB update, fix SphereHeightfield transform.
Sph: add ~2ms faster OpenCL neighbor query.

65536 particles, Radeon 5850, OpenCL grid update enabled;
btFluidSphSolverOpenCL::updateGridAndCalculateSphForces(): 14ms -> 12ms