Switch back to using __block std::vector variables; previous crashes were cause by mis-allocated dlist.
Undo switch back to using __block std::vector variables; previous commit re-introduced memory corruption.
Finally fix __block std::vector<int> dlist(m, depth); also fixes a subtle incompatibility with the depth parameter.
Initial check-in of vMAT_numel function, plus some progress on vMAT_cluster.