isolates refactor: this change introduces 'dart:isolate' as a library. This is a

compiler/lib/corelib.dart

 #!/usr/bin/env dart
 // Copyright (c) 2011, 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.
 
 #library("corelib");
 #import("corelib_impl.dart");
 
 #source("clock.dart");
 #source("error.dart");
 #source("object.dart");
 #source("print.dart");
 #source("src/bool.dart");
 #source("src/collection.dart");
 #source("src/comparable.dart");
 #source("src/date.dart");
 #source("src/double.dart");
 #source("src/duration.dart");
 #source("src/exceptions.dart");
 #source("src/expect.dart");
 #source("src/function.dart");
 #source("src/future.dart");
 #source("src/hashable.dart");
 #source("src/int.dart");
-#source("src/isolate.dart");
 #source("src/iterable.dart");
 #source("src/iterator.dart");
 #source("src/list.dart");
 #source("src/map.dart");
 #source("src/math.dart");
 #source("src/num.dart");
 #source("src/pattern.dart");
 #source("src/queue.dart");
 #source("src/regexp.dart");
 #source("src/set.dart");
 #source("src/stopwatch.dart");
 #source("src/string.dart");
 #source("src/strings.dart");
 #source("src/string_buffer.dart");
 #source("src/time_zone.dart");
 #source("coverage.dart");