Fixed a test failure under Postgres caused by primary key sequence allocation.

>>> t4 = Tag.objects.create(name='t4', parent=t3)

>>> t5 = Tag.objects.create(name='t5', parent=t3)

>>> n1 = Note.objects.create(note='n1', misc='foo')

>>> n2 = Note.objects.create(note='n2', misc='bar')

>>> n3 = Note.objects.create(note='n3', misc='foo')

>>> n1 = Note.objects.create(note='n1', misc='foo', id=1)

>>> n2 = Note.objects.create(note='n2', misc='bar', id=2)

>>> n3 = Note.objects.create(note='n3', misc='foo', id=3)

>>> ann1 = Annotation.objects.create(name='a1', tag=t1)

>>> ann1.notes.add(n1)