Fix various pub issues.

lib/src/pubspec.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.
 
 library pub.pubspec;
 
 import 'package:path/path.dart' as path;
 import 'package:pub_semver/pub_semver.dart';
 import 'package:source_span/source_span.dart';
 import 'package:yaml/yaml.dart';
@@ skipping 294 matching lines @@
   /// Loads the pubspec for a package located in [packageDir].
   ///
   /// If [expectedName] is passed and the pubspec doesn't have a matching name
   /// field, this will throw a [PubspecError].
   factory Pubspec.load(String packageDir, SourceRegistry sources,
       {String expectedName}) {
     var pubspecPath = path.join(packageDir, 'pubspec.yaml');
     var pubspecUri = path.toUri(pubspecPath);
     if (!fileExists(pubspecPath)) {
       throw new FileException(
-          'Could not find a file named "pubspec.yaml" in "$packageDir".',
+          // Make the package dir absolute because for the entrypoint it'll just
+          // be ".", which may be confusing.
+          'Could not find a file named "pubspec.yaml" in '
+              '"${path.normalize(path.absolute(packageDir))}".',
           pubspecPath);
     }
 
     return new Pubspec.parse(readTextFile(pubspecPath), sources,
         expectedName: expectedName, location: pubspecUri);
   }
 
   Pubspec(this._name, {Version version, Iterable<PackageDep> dependencies,
           Iterable<PackageDep> devDependencies,
           Iterable<PackageDep> dependencyOverrides,
@@ skipping 248 matching lines @@
     implements ApplicationException {
   PubspecException(String message, SourceSpan span)
       : super(message, span);
 }
 
 /// Returns whether [uri] is a file URI.
 ///
 /// This is slightly more complicated than just checking if the scheme is
 /// 'file', since relative URIs also refer to the filesystem on the VM.
 bool _isFileUri(Uri uri) => uri.scheme == 'file' || uri.scheme == '';