Fixed #7350, #7202 -- Fixed serialization for multi-model inheritance, which had multiple problems:

 * Serializers were including all superclass fields in their output. Now only local fields are included.
 * Implicit OneToOne primary keys were not correctly added to the metamodel, so they were always marked to be serialized, even though they were primary
 * Model saving was too aggressive about creating new parent class instances during deserialization. Raw save on a model now skips saving of the parent class.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@7600 bcc190cf-cafb-0310-a4f2-bffc1f526a37