Clean up the semantics of io.dart operations w.r.t. symlinks.

utils/tests/pub/install/pub_install_test.dart

Index: utils/tests/pub/install/pub_install_test.dart
diff --git a/utils/tests/pub/install/pub_install_test.dart b/utils/tests/pub/install/pub_install_test.dart
index bdaa25fd18a350ab4246bb1f56fac7c65563042f..f927b54b8f13ac5a682bc244bb8d9f405bc3621c 100644
--- a/utils/tests/pub/install/pub_install_test.dart
+++ b/utils/tests/pub/install/pub_install_test.dart
@@ -6,8 +6,10 @@ library pub_tests;
 
 import 'dart:io';
 
+import '../../../../pkg/pathos/lib/path.dart' as path;
 import '../../../../pkg/scheduled_test/lib/scheduled_test.dart';
 
+import '../../../pub/io.dart';
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 
@@ -114,6 +116,29 @@ main() {
     ]).validate();
   });
 
+  integration('overwrites a broken packages directory symlink', () {
+    d.dir(appPath, [
+      d.appPubspec([]),
+      d.dir('packages'),
+      d.libDir('myapp'),
+      d.dir('bin')
+    ]).create();
+
+    scheduleSymlink(
+        path.join(appPath, 'packages'),
+        path.join(appPath, 'bin', 'packages'));
+
+    schedule(() => deleteEntry(path.join(sandboxDir, appPath, 'packages')));
+
+    schedulePub(args: ['install'],
+        output: new RegExp(r"Dependencies installed!$"));
+
+    d.dir(packagesPath, [
+      d.nothing('foo'),
+      d.dir('myapp', [d.file('myapp.dart', 'main() => "myapp";')])
+    ]).validate();
+  });
+
   group('creates a packages directory in', () {
     integration('"test/" and its subdirectories', () {
       d.dir(appPath, [