Added blurbs to the model unit tests that didn't have them

"""

23. Giving models a custom manager

You can use a custom ``Manager`` in a particular model by extending the base

``Manager`` class and instantiating your custom ``Manager`` in your model.

There are two reasons you might want to customize a ``Manager``: to add extra

``Manager`` methods, and/or to modify the initial ``QuerySet`` the ``Manager``

returns.

"""

from django.db import models

    def __repr__(self):

        return "%s %s" % (self.first_name, self.last_name)

# An example of a custom manager that sets a core_filter on its lookups.

# An example of a custom manager that sets get_query_set().

class PublishedBookManager(models.Manager):

    def get_query_set(self):

"""

26. A test to check that the model validator works can correctly identify errors in a model. 

26. Invalid models

This example exists purely to point out errors in models.

"""

from django.db import models

"""

25. Default manipulators

Each model gets an AddManipulator and ChangeManipulator by default.

"""

from django.db import models

"""

XX. Model inheritance

Model inheritance isn't yet supported.

"""

from django.db import models

"""

22. Using properties on models

Use properties on models just like on any other Python object.

"""

from django.db import models