s the specified PO files.
Find messages which are common to two or more of the specified PO files.
By using the --more-than option, greater commonality may be requested
before messages are printed.  Conversely, the --less-than option may be
used to specify less commonality before messages are printed (i.e.
--less-than=2 will only print the unique messages).  Translations,
comments, extracted comments, and file positions will be cumulated, except
that if --use-first is specified, they will be taken from the first PO file
to define them.