Fixture id of zero should not be raise an undefined id property error.
Remove empty line.
Raise error for invalid fixture id types.
Update test to expect updated error message.
Promises Step 1: Use promises instead of callbacks
This step was a small step, merely to swap out
callbacks for promises at the adapter level.
Subsequent steps will result in more aggressive
refactoring, and begin to fully use promises.

@stefanpenner & @leepfrog aka 'the leeping Penner'

Bonus:
```Model.find#then``` now rejects/resolves correctly.
_deferred and promise should not be accessed outside the mixin
Merge pull request #3 from teddyzeenny/load-promise

_deferred and promise should not be accessed outside the mixin
Merge branch 'master' of https://github.com/emberjs/data

Conflicts:
	packages/ember-data/lib/adapters/rest_adapter.js
Merge pull request #934 from stefanpenner/promisify

Promises Step 1: Use promises instead of callbacks
Only coerce belongsTo ids to string if id is defined
Fix RestAdapter#ajax
Merge pull request #938 from teddyzeenny/fix-ajax

Fix RestAdapter#ajax to account for empty hash
use store#recordWasError hook
Merge pull request #939 from tchak/became-error

use store#recordWasError hook
Merge pull request #937 from teddyzeenny/fixture-belongs-to

Only coerce belongsTo ids to string if id is defined
embedded associations are now automatically added to the parent's transaction
This PR represents a lot of refactor work on the rest_adapter_test unit tests.

All of the tests which are passing have been modified to match their original passing conditions. There is one failing test included (which I believe is legitimate), that uncovers an issue with sideloading data.

Summary of changes:
- added flagEquals / stateEquals assertion helpers
- added comments for test helpers
- removed teardown for tests (all tests remained green after doing so)
- cleaned up scoping for tests -- globals only used for configuration, locals used for test data
- relocated helper functions to top of test
- removed unnecessary var definitions
- created a consistent test format:
- test setup code is grouped together
- test assertion code is grouped together
- whitespace between setup and assertion code
- comments above each individual assertion and setup block
- each test should have a state and flag assertion after a model change state

The new flagEquals() assertions and stateEquals() assertions should probably be audited to ensure that the state of the records should actually be what the assertion says they are. While re-writing these tests, I personally disagree with some of the flags set for the given record states.
Fix rest adapter failing tests
Merge pull request #1 from teddyzeenny/reset-adapter-tests

Fix rest adapter failing tests
remove transaction-level relationship book-keeping