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
Fix belongsTo relationships to models with id 0
Merge pull request #876 from tricknotes/fix-belongs-to-relationships

Fix belongsTo relationships to models with id 0
Remove unused local variable
Merge pull request #877 from tricknotes/remove-unused

Remove unused local variable
Merge pull request #812 from zachriggle/master

Move createSerializedForm to DS.Serializer
Allow options.defaultValue of DS.attr to be a function

This change allows the defaultValue defined for a DS.attr to be a
function, so it is possible to do something like this:

```
User = DS.Model.extend({
  createdAt: DS.attr("date", {
    defaultValue: function() {
      return (new Date());
    }
  })
});
```

This closes #878
Remove duplicate #createSerializedForm method from DS.Serializer
Merge pull request #880 from pangratz/remove_duplicate_createSerializedForm

Remove duplicate #createSerializedForm method from DS.Serializer
Typo in Bulk DELETE test

This test labeled as issuing a `PUT` instead of a `DELETE`

The actual test code does make a `DELETE` request
Merge pull request #882 from southpolesteve/patch-1

Typo in Bulk DELETE test
Merge pull request #879 from pangratz/allow_function_as_default_value

Allow options.defaultValue of DS.attr to be a function
Merge pull request #747 from fpauser/isloading-flag

Add 'isLoading' flag to DS.State
A record is found after loading its id through a hasMany relationship.

As we have now a reference for records in a hasMany relationship,
we need to make sure we load them when accessed. If the record is
`UNLOADED`, we materialize the record.

[Fixes #869]
Merge pull request #883 from Cyril-sf/has-many-bug

A record is found after loading its id through a hasMany relationship.