Made CommandError use the exception directive in docs.

The ``handle()`` method takes one or more ``poll_ids`` and sets ``poll.opened``

to ``False`` for each one. If the user referenced any nonexistent polls, a

:class:`CommandError` is raised. The ``poll.opened`` attribute does not exist

in the :doc:`tutorial</intro/tutorial01>` and was added to

``polls.models.Poll`` for this example.

:exc:`CommandError` is raised. The ``poll.opened`` attribute does not exist in

the :doc:`tutorial</intro/tutorial01>` and was added to ``polls.models.Poll``

for this example.

.. _custom-commands-options:

    This option can't be ``False`` when the

    :data:`~BaseCommand.can_import_settings` option is set to ``False`` too

    because attempting to set the locale needs access to settings. This

    condition will generate a :class:`CommandError`.

    condition will generate a :exc:`CommandError`.

.. attribute:: BaseCommand.style

    Tries to execute this command, performing system checks if needed (as

    controlled by the :attr:`requires_system_checks` attribute). If the command

    raises a :class:`CommandError`, it's intercepted and printed to stderr.

    raises a :exc:`CommandError`, it's intercepted and printed to stderr.

.. admonition:: Calling a management command in your code

.. method:: BaseCommand.check(app_configs=None, tags=None, display_num_errors=False)

    Uses the system check framework to inspect the entire Django project for

    potential problems. Serious problems are raised as a :class:`CommandError`;

    potential problems. Serious problems are raised as a :exc:`CommandError`;

    warnings are output to stderr; minor notifications are output to stdout.

    If ``app_configs`` and ``tags`` are both ``None``, all system checks are

    Perform the command's actions for ``label``, which will be the string as

    given on the command line.

.. _ref-command-exceptions:

Command exceptions

------------------

.. class:: CommandError

.. exception:: CommandError

Exception class indicating a problem while executing a management command.

    django-admin migrate --traceback

By default, ``django-admin`` will show a simple error message whenever a

:class:`~django.core.management.CommandError` occurs, but a full stack trace

:exc:`~django.core.management.CommandError` occurs, but a full stack trace

for any other exception. If you specify ``--traceback``, ``django-admin``

will also output a full stack trace when a ``CommandError`` is raised.

* Management commands do not raise ``SystemExit`` any more when called by code

  from :ref:`call_command <call-command>`. Any exception raised by the command

  (mostly :ref:`CommandError <ref-command-exceptions>`) is propagated.

  (mostly :exc:`~django.core.management.CommandError`) is propagated.

  Moreover, when you output errors or messages in your custom commands, you

  should now use ``self.stdout.write('message')`` and

  to manually delete objects from deleted forms.

* Loading empty fixtures emits a ``RuntimeWarning`` rather than raising

  :class:`~django.core.management.CommandError`.

  :exc:`~django.core.management.CommandError`.

* :func:`django.contrib.staticfiles.views.serve` will now raise an

  :exc:`~django.http.Http404` exception instead of