fop(1): better opt matching

src/fop.rs

@@ -42,12 +42,12 @@ fn main() {
 
 	while let Some(opt) = argv.getopt("d:") {
 		match opt.opt() {
-			Ok(_) => {
+			Ok("d") => {
 				/* delimiter */
 				d = opt.arg().unwrap();
 				optind = opt.ind();
 			},
-			Err(_) => {
+			_ => {
 				eprintln!("{}", usage);
 				exit(EX_USAGE);
 			}