(check_file): Generate each line of output earlier,

(check_file): Generate each line of output earlier,
when possible.  It is possible when using none of these options:
--count, -repeated, --all-repeated, --unique.
Based on a patch from Ian Turner.

(check_file): Move declarations of local variables into the scopes where used.
(min): Remove macro definition.
(different): Use MIN, not min.
(SWAP_LINES): New macro.
(check_file): Use it here.