Blocking for MH

MH has now grid-like book keeping of point locations for faster R-closeness determination.

Not yet for dCFTP and BD as death removes from the stack and book keeping uses stack indices, meaning that each death requires index re-aligning (costly).

Could be made faster by pointers to blocking, now with if's.

Also changed:

* Distances are now computed using distLessThan-functions, slight speed gain if neighbour not in R-cube.