Add tests for calling jQuery.ajax from DS.RESTAdapter
Fix: unload record with relationships

- calling `clearRelationships` before changing record state,
  otherwise it fails, because properties try to update removed
  relationships

- Transaction commit failed when an unloaded record was in the
  `transaction.bucketForType.updated` array. Using recordIsMoving fixed
  this issue
Only setting content-type to JSON if there actually is content.
Merge branch 'master' of github.com:enyo/data
Added a test for the content-type.
fix test description
Warn if an application lacks a Store property

Attempts to use model class related methods that alias
to the store currently throw
`TypeError: Cannot read property 'find' of undefined`

This commit improves the message and offers a suggested
solution.
Fixed trailing commas which breaks IE7.
fixed issue #582
added adapter integration test for dirtyRecordsForAttributeChange
Introduce a custom `keyForHasMany()` for `DS.RESTSerializer`.

This method returns the singularized key appended with `_ids`. It uses the same plurals hash on the serializer to determine singular versions of keys.

Fixes #710
Failing test: 'When a record is loaded a second time, isLoaded should stay true'
Merge pull request #727 from dgeb/rest-adapter-has-many-ids

Introduce a custom `keyForHasMany()` for `DS.RESTSerializer`.
Add missing suspendRelationshipsObservers for belongsTo in ChangeRemove
Merge pull request #715 from sandstrom/relationship-change-remove-belongs-to-loop

Add missing `suspendRelationshipsObservers` for belongsTo in DS.RelationshipChangeRemove
Warn, don't fail, when there are no fixtures
Fail rather than returning all fixtures when queryFixtures is not implemented
Add docs directory with package.json and yuidoc.json

`EMBER_PATH=../ember-data rake preview` in ember-website does not quite
work yet. I don't have time at the moment to get it working completely,
but let's have the docs directory as a starting point.
Use Ember.run.later instead of setTimeout in FixtureAdapter
Be asynchronous (though deterministic) when simulateRemoteResponse is false

It's not clear that there is really a use case for synchronous responses
in FixtureAdapter. Asynchronous responses on the other hand are much
preferable for realistic testing.