Updating to work on Dart 1.4.0-dev.2

Pub in 1.4 is requiring barback 1.3 which has a breaking change in isPrimary (see https://codereview.chromium.org//223553008). Code_transformers has been updated to be compatible with both Dart 1.3 (stable) and Dart 1.4 (dev).

This incorporates those changes to allow DI to run on 1.3 and 1.4-dev.
Merge pull request #83 from blois/dart1.4_dev

Updating to work on Dart 1.4.0-dev.2