PackedBoolList specializaton for operator=

- now that I re-examined the code, the note in commit 51fd6327
  can be mostly ignored

  PackedList isMaster(nPoints, 1u);
  is not really inefficient at all, since the '1u' is packed into
  32/64-bits before the subsequent assignment and doesn't involve
  shifts/masking for each index

  The same misinformation applies to the PackedList(size, 0u) form.
  It isn't much slower at all.

  Nonetheless, add bool specialization so that it is a simple assign.