Split up "diff_format" into "format" and "line_termination".

This removes the separate "formats" for name and name-with-zero-
termination.

It also removes the difference between HUMAN and MACHINE formats, and
they both become DIFF_FORMAT_RAW, with the difference being just in the
line and inter-filename termination.

It also makes the code easier to understand.

diff-helper.c

@@ -17,7 +17,7 @@ static void flush_them(int ac, const char **av)
 	diffcore_std_no_resolve(av + 1,
 				pickaxe, pickaxe_opts,
 				orderfile, diff_filter);
-	diff_flush(DIFF_FORMAT_PATCH);
+	diff_flush(DIFF_FORMAT_PATCH, '\n');
 }
 
 static const char *diff_helper_usage =