original commit log by miller@OpenBSD r1.46:
Fix exit value when diffing directories with missing files and the -N
or -P options are not used. From Ibrahim Khalifa
i.e., when print_only is called.
Prior to this change, -rq was always returning 0. After this change it will
return 1 if there is a difference between two directories.
This fixes compatibility with GNU diff and unbreaks backwards compatibility
expectations.
Found when trying to extend diff_test:brief_format_test.
MFC after: 2 months
MFC with: r321076, r321077
Some of the modifications from the previous summer of code has been integrated
Modification for compatibility with GNU diff output has been added
Main difference with OpenBSD:
Implement multiple GNU diff options:
* --ignore-file-name-case
* --no-ignore-file-name-case
* --normal
* --tabsize
* --strip-trailing-cr
Make diff -p compatible with GNU diff
Implement diff -l
Make diff -r compatible with GNU diff
Capsicumize diffing 2 regular files
Add a simple test suite
Approved by: AsiaBSDcon devsummit
Obtained from: OpenBSD, GSoC
Relnotes: yes
