Enable features selected for next beta cycle.

The following features have been selected by the core team as being
ready to go for the next beta cycle. As such, they should be enabled on
all canary builds to ensure they are stable.

See https://github.com/emberjs/ember.js/issues/4052 for details.
Merge pull request #4061 from rjackson/enabled_goed_features

Enable features selected for next beta cycle.