Follow ReferenceFields in EmbeddedDocuments with select_related

For the following structure:

    class Playlist(Document):
        items = ListField(EmbeddedDocumentField("PlaylistItem"))

    class PlaylistItem(EmbeddedDocument):
        song = ReferenceField("Song")

    class Song(Document):
        title = StringField()

this patch prevents the N+1 queries otherwise required to fetch all
the `Song` instances referenced by all the `PlaylistItem`s.
Merge pull request #690 from claymation/select-related

Follow ReferenceFields in EmbeddedDocuments with select_related
Fix tests for Django 1.7
Update AUTHORS
Prevent accessing not yet configured settings in django.MongoTestCase
Fix MongoTestCase and add test for it
Fix MongoTestCase and add test for it
Update changelog
Merge pull request #696 from lexqt/fix_django_17_compat

Fix tests for django 1.7
merge with origin done