Mechanism for writing a status message in a loop

[sigvaldm]

Nice for instance for debug diagnostics. Message may perhaps come after task legend or instead of it.

[sigvaldm]

To clarify: Sometimes during debugging you would just like to print a number for each timestep, and see how it evolves. It would still be the same task, though, so using timer.task() is not a good hack, since it change the task. Perhaps timer.task could take a string which is not supposed to be part of the task?