Fix some doc comments that didn't use Markdown syntax for code blocks.

lib/core/future.dart

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * A [Future] is used to obtain a value sometime in the future.  Receivers of a
  * [Future] can obtain the value by passing a callback to [then]. For example:
  *
  *     Future<int> future = getFutureFromSomewhere();
  *     future.then((value) {
  *       print("I received the number $value");
@@ skipping 126 matching lines @@
   Future transformException(transformation(Object exception));
 }
 
 /**
  * A [Completer] is used to produce [Future]s and supply their value when it
  * becomes available.
  *
  * A service that provides values to callers, and wants to return [Future]s can
  * use a [Completer] as follows:
  *
- *   Completer completer = new Completer();
- *   // send future object back to client...
- *   return completer.future;
- *   ...
+ *     Completer completer = new Completer();
+ *     // send future object back to client...
+ *     return completer.future;
+ *     ...
  *
- *   // later when value is available, call:
- *   completer.complete(value);
+ *     // later when value is available, call:
+ *     completer.complete(value);
  *
- *   // alternatively, if the service cannot produce the value, it
- *   // can provide an exception:
- *   completer.completeException(exception);
+ *     // alternatively, if the service cannot produce the value, it
+ *     // can provide an exception:
+ *     completer.completeException(exception);
  *
  */
 interface Completer<T> default CompleterImpl<T> {
 
   Completer();
 
   /** The future that will contain the value produced by this completer. */
   Future get future;
 
   /** Supply a value for [future]. */
@@ skipping 62 matching lines @@
       future.handleException((exception) {
         if (!result.isComplete) {
           completer.completeException(exception, future.stackTrace);
         }
         return true;
       });
     }
     return result;
   }
 }