Removed future's destructor

It was only there to prevent Future from being copyable, but it's
noncopyable anyways since it contains a ~fn.

src/libextra/future.rs

@@ -37,15 +37,6 @@ pub struct Future<A> {
     priv state: FutureState<A>,
 }
 
-// n.b. It should be possible to get rid of this.
-// Add a test, though -- tjc
-// FIXME(#2829) -- futures should not be copyable, because they close
-// over ~fn's that have pipes and so forth within!
-#[unsafe_destructor]
-impl<A> Drop for Future<A> {
-    fn drop(&mut self) {}
-}
-
 enum FutureState<A> {
     Pending(~fn() -> A),
     Evaluating,

src/test/compile-fail/future_not_copyable.rs

@@ -0,0 +1,19 @@
+// Copyright 2013 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.
+
+extern mod extra;
+
+use extra::future;
+
+fn main() {
+    let f = future::from_value(());
+    let g = f;
+    f.unwrap(); //~ ERROR use of moved value
+}