Fix --offline with prerelease versions.

test/hosted/offline_test.dart

 // 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.
 
 import 'package:pub/src/exit_codes.dart' as exit_codes;
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 main() {
@@ skipping 19 matching lines @@
       }
 
       pubCommand(command, args: ['--offline'], warning: warning);
 
       d.packagesDir({
         "foo": "1.2.3",
         "bar": "1.2.3"
       }).validate();
     });
 
+    integration('supports prerelease versions', () {
+      // Run the server so that we know what URL to use in the system cache.
+      serveErrors();
+
+      d.cacheDir({
+        "foo": ["1.2.3-alpha.1"]
+      }, includePubspecs: true).create();
+
+      d.appDir({
+        "foo": "any"
+      }).create();
+
+      var warning = null;
+      if (command == RunCommand.upgrade) {
+        warning = "Warning: Upgrading when offline may not update you "
+                  "to the latest versions of your dependencies.";
+      }
+
+      pubCommand(command, args: ['--offline'], warning: warning);
+
+      d.packagesDir({
+        "foo": "1.2.3-alpha.1"
+      }).validate();
+    });
+
     integration('fails gracefully if a dependency is not cached', () {
       // Run the server so that we know what URL to use in the system cache.
       serveErrors();
 
       d.appDir({"foo": "any"}).create();
 
       pubCommand(command, args: ['--offline'],
           exitCode: exit_codes.UNAVAILABLE,
           error: "Could not find package foo in cache.\n"
                  "Depended on by:\n"
@@ skipping 42 matching lines @@
       d.appDir({"foo": "any"}).create();
 
       createLockFile('myapp', hosted: {'foo': '1.2.4'});
 
       pubCommand(command, args: ['--offline']);
 
       d.packagesDir({"foo": "1.2.3"}).validate();
     });
   });
 }