enableIsDirty breaks when used with ember-data-model-fragments

[wizbyt]

Setting enableIsDirty whilst using ember-data-model-fragments and changing any belongsTo or hasMany relationship doesn't change any of the flags on a model.

Any changes to the relationships on a model leave the flags as false:

hasDirtyAttributes: false
hasDirtyRelations: false
isDirty: false

Removing the enableIsDirty configuration option makes the "hasDirtyAttributes" flag work again.

I'm not sure whether the problem is with ember-data-change-tracker or ember-data-model-fragments.

[danielspaniel]

sorry for late reply @wizbyt .. do you think you can write up a test in a PR ?