- make sizing of commsStruct List demand-driven as well
for more robustness, fewer unneeded allocations.
- fix potential latent bug with allBelow/allNotBelow for proc 0
(linear communication).
ENH: remove unused/unusable UPstream::communicator optional parameter
- had constructor option to avoid constructing the MPI backend,
but this is not useful and inconsistent with what the reset or
destructor expect.
STYLE: local use of UPstream::communicator
- automatically frees communicator when it leaves scope
9d3427e0b4