Split the diff tests to get finer grained failures. Also cleaned up some unused imports.
Remove duplication in cleanups. Note that --forward-ed is not in diff 3.3 and may need to be removed from the supported options.
Doh, this is *still* supported by diff 3.3 (just not documented in the man page nor the online help anymore).
(vila) Split some tests to be able to get finer grained failures (Vincent
 Ladeuil)