[bug] diff is not SUSv3-compliant

[Laurent Bercot]

 Hi,

 SUSv3 requires diff to support the -c, -e, -f, and -C n options:
<URL: http://www.opengroup.org/onlinepubs/000095399/utilities/diff.html >

 As of 1.18.4, busybox diff does not support those options.

 SUSv4 also requires the -U n option (which is supported) and the -u one
(which is not - but it's trivial to add since it's equivalent to -U 3).

 I don't think it is really important to add the -e and -f options, unless
someone can provide a real-world usage example. However, the -c option
would be nice to have, because "diff -c" is used in GNU autoconf-generated
configure scripts.

 Thanks,

-- 
 Laurent