3.2.6. Debug printout

For largely historic reasons the code still contains a lot of debugging and diagnostic print messages, typically controlled by a local verbose parameter, similar to:

if (verbose > 0) then
  write (io_unit%log,'(....)') &
    wallclock(), ...
  if (verbose > 1) then
    ...
  end if
end if

Because many such code blocks can be very detrimental to code readability this is discouraged (meaning most of those constructs will be gradually removed), in favor of adding ad hoc statements of the type (fully left-adjusted, to stand out)::

write (stderr,*) wallclock(), mpi%rank, omp%thread, 'message', task%id

specifically tracing some action through various pieces of the code, to be removed after filling their function. The lines should be removed in a dedicated commit, so they are recoverable via a simple git revert, w/o introducing other changes.