Run pub if there's a pubspec.yaml in the code/ subdir when running article tests.
tests for Shailen's basic Futures article

Review URL: https://chromiumcodereview.appspot.com/12971002
test the style guide

staged at http://testable-docs.dart-lang.appspot.com/

BUG=

Review URL: https://chromiumcodereview.appspot.com//12927005
Merge pull request #48 from timothyarmstrong/test-article-pub-support

Run pub when necessary for testing articles