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
fixed issue #582
added adapter integration test for dirtyRecordsForAttributeChange
Failing test: 'When a record is loaded a second time, isLoaded should stay true'
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.
Add live query test for RecordArray
Potential fix for #731
Use Ember.isNone for null check instead of !

Using !id to check for a null belongsTo id was causing relationships to be treated as missing.
Remove unused method

DS.Model#setProperty is no longer working.
Fix typo in addRelationships documentation
Move createSerializedForm to DS.Serializer.  Serializer calls the routine currently, but it's only defined in the JSON and Fixture implementations.
Added 'isLoading' flag to DS.State
Add assertion in `relatedTypes` to catch undefined relations
pushData and load now call loadData instead of duplicating code
Add assertion on BasicAdapter.findHasMany