etcupdate(8) requires that option, while GNU diff supports many more variation
of that options, their behaviour beside the simple verion implemented here are
quite inconsistent as such I do not plan to implement those.
The only special keyword supported by this implementation are: %< and %>
%= is not implemented as the documentation of GNU diff says: common lines, but
it actually when tested print the changes from the first file
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
