Allow to copy untouched files rather than rewrite them
Practically we may often want to rewrite only those files affected by reduction and copy the untouched files verbatim to avoid the extensive cost of rewriting. This is particularly excessive as often aggregators with few INSTRUMENT
sources will get rewritten while those with many CONTORL
sources remain untouched.
This MR adds a flag --output-untouched-copy
that allows to automatically make a verbatim copy of untouched aggregator files instead. It only works with --output-scope all --output-layout collection
and is ignored otherwise with a warning.