Allreduce using bcube algorithm caveats

[pietern]

The comments mention it is usable for any #nodes == c * base ^ x, for any c >= 1, base >= 2, and x >= 1, but in reality there is another constraint, namely c < base. If c > base hypercube won't be connected as expected, and yields incorrect results.

This algorithm is being reimplemented anyway to support any factorization of #nodes, but leaving this observation here for posterity.