added temporary logging
Process equidistant narrow band points in parallel.

A possible solution to the symmetry problem: freeze batches of points
which are equidistant from the front simultaneously and update all of
their neighbors all at once.

This is just an experiment, using std::vector like this causes heap
thrash.
remove logging
Clarifying comment about baseMarcher::_getN()
Merge remote-tracking branch 'remotes/origin/logging'