libstd: Add Fn/FnMut/FnOnce to the prelude.

Closes #16600.

src/libstd/prelude.rs

@@ -46,6 +46,7 @@
 #[doc(no_inline)] pub use ops::{Drop, Deref, DerefMut};
 #[doc(no_inline)] pub use ops::{Shl, Shr};
 #[doc(no_inline)] pub use ops::{Index, IndexMut};
+#[doc(no_inline)] pub use ops::{Fn, FnMut, FnOnce};
 #[doc(no_inline)] pub use option::{Option, Some, None};
 #[doc(no_inline)] pub use result::{Result, Ok, Err};
 

src/test/run-pass/unboxed-closures-prelude.rs

@@ -0,0 +1,19 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Tests that the reexports of `FnOnce` et al from the prelude work.
+
+#![feature(unboxed_closures, unboxed_closure_sugar)]
+
+fn main() {
+    let task: Box<|: int| -> int> = box |: x| x;
+    task.call_once((0i, ));
+}
+