Remove an extraneous comma that I left behind in [7386], and clean up the wording a bit more.

Allows the selection of a single model object, suitable for

representing a foreign key.

The labels for the choice field call the ``__unicode__`` method of the

model to generate string representations to use in the field's

choices; to provide customized representations,, subclass

``ModelChoiceField`` and override ``label_for_model``; this method

will receive an object, and should return a string suitable for

representing it::

The ``__unicode__`` method of the model will be called to generate

string representations of the objects for use in the field's choices;

to provide customized representations, subclass ``ModelChoiceField``

and override ``label_for_model``. This method will receive model

object, and should return a string suitable for representing it::

    class MyModelChoiceField(ModelChoiceField):

        def label_from_instance(self, obj):