std and green: fix some warnings

src/libgreen/sched.rs

@@ -1473,7 +1473,7 @@ mod test {
             let mut handle = pool.spawn_sched();
             handle.send(PinnedTask(pool.task(TaskOpts::new(), proc() {
                 unsafe {
-                    let mut guard = LOCK.lock();
+                    let guard = LOCK.lock();
 
                     start_tx.send(());
                     guard.wait();   // block the scheduler thread
@@ -1509,7 +1509,7 @@ mod test {
                 child_tx.send(20);
                 pingpong(&parent_rx, &child_tx);
                 unsafe {
-                    let mut guard = LOCK.lock();
+                    let guard = LOCK.lock();
                     guard.signal();   // wakeup waiting scheduler
                     guard.wait();     // wait for them to grab the lock
                 }

src/libstd/iter.rs

@@ -2335,7 +2335,7 @@ mod tests {
 
     #[test]
     fn test_counter_from_iter() {
-        let mut it = count(0, 5).take(10);
+        let it = count(0, 5).take(10);
         let xs: ~[int] = FromIterator::from_iterator(it);
         assert_eq!(xs, ~[0, 5, 10, 15, 20, 25, 30, 35, 40, 45]);
     }

src/libstd/str.rs

@@ -3218,7 +3218,7 @@ mod tests {
         let data = ~"ประเทศไทย中";
         let mut cpy = data.clone();
         let other = "abc";
-        let mut it = other.chars();
+        let it = other.chars();
         cpy.extend(it);
         assert_eq!(cpy, data + other);
     }

src/libstd/unstable/mutex.rs

@@ -621,7 +621,7 @@ mod test {
     #[test]
     fn destroy_immediately() {
         unsafe {
-            let mut m = StaticNativeMutex::new();
+            let m = StaticNativeMutex::new();
             m.destroy();
         }
     }