[BUGFIX beta] Deprecate quoteless action names.

This is preparation for enabling the `ember-routing-bound-action-name` feature.

As requested by @tomdale in https://github.com/emberjs/ember.js/pull/3936#issuecomment-33835794.

This should be pulled into the current 1.4.0 beta series, so that we can enable `ember-routing-bound-action-name` in the 1.5.0 beta series.