Merge branch 'jk/diff-convfilter-test-fix'

* jk/diff-convfilter-test-fix:
  Avoid using non-portable `echo -n` in tests.
  add userdiff textconv tests
  document the diff driver textconv feature
  diff: add missing static declaration

Conflicts:
	Documentation/gitattributes.txt

diff.c

@@ -1283,7 +1283,7 @@ static void emit_binary_diff(FILE *file, mmfile_t *one, mmfile_t *two)
 	emit_binary_diff_body(file, two, one);
 }
 
-void diff_filespec_load_driver(struct diff_filespec *one)
+static void diff_filespec_load_driver(struct diff_filespec *one)
 {
 	if (!one->driver)
 		one->driver = userdiff_find_by_path(one->path);