Turned extra::getopts functions into methods

Some minor api and doc adjustments

src/test/bench/shootout-pfib.rs

@@ -64,7 +64,7 @@ fn parse_opts(argv: ~[~str]) -> Config {
 
     match getopts::getopts(opt_args, opts) {
       Ok(ref m) => {
-          return Config {stress: getopts::opt_present(m, "stress")}
+          return Config {stress: m.opt_present("stress")}
       }
       Err(_) => { fail!(); }
     }

src/test/run-pass/getopts_ref.rs

@@ -20,8 +20,8 @@ pub fn main() {
 
     match getopts(args, opts) {
         Ok(ref m)  =>
-            assert!(!opt_present(m, "b")),
-        Err(ref f) => fail!(fail_str((*f).clone()))
+            assert!(!m.opt_present("b")),
+        Err(ref f) => fail!((*f).clone().to_err_msg())
     };
 
 }