Properly chain preprocessing plugins.
Merge pull request #1987 from rwjblue/properly-chain-plugins

Properly chain preprocessing plugins.
Ensure that registry plugins added manually can be returned.
Merge pull request #1993 from rwjblue/allow-registered-plugins-to-not-be-in-package-json

Ensure that registry plugins added manually can be returned.
Fix model-test blueprint.

Passing a model (anything with a `toJSON` actually) into a test
assertion causes infinite loop with Testem.

Steps:

* Do an assert in your test like ok(store.find('person', 1), "record
  exists")
* QUnit stores the assertion in a test object.
* The test finishes so the record is destroyed automatically.
* QUnit notifies listeners the test is over.
* Testem listens for test end notification and attempts to ensure that
  there are no cycles in it by calling `JSON.parse(JSON.stringify(testObject))`.
* Calls `toJSON()` recursively, including any destroyed object that was
  used in an assertion.

Watch as tests hang when running ember test but work fine everywhere else.
Merge pull request #1996 from rwjblue/fix-model-tests

Fix model-test blueprint.
Refactor addon fixtures.

Migrate to currently suggested exporting of an object.
Merge pull request #1995 from rwjblue/refactor-addon-tests

Refactor addon fixtures.
added pod blueprints and tests