Add --dry-run option to makemigrations

class Command(BaseCommand):

    option_list = BaseCommand.option_list + (

        make_option('--empty', action='store_true', dest='empty', default=False,

            help='Make a blank migration.'),

        make_option('--dry-run', action='store_true', dest='dry_run', default=False,

            help="Just show what migrations would be made; don't actually write them."),

    )

    help = "Creates new migration(s) for apps."

    usage_str = "Usage: ./manage.py makemigrations [--empty] [app [app ...]]"

    usage_str = "Usage: ./manage.py makemigrations [--dry-run] [app [app ...]]"

    def handle(self, *app_labels, **options):

        self.verbosity = int(options.get('verbosity'))

        self.interactive = options.get('interactive')

        self.dry_run = options.get('dry_run', False)

        # Make sure the app they asked for exists

        app_labels = set(app_labels)

                    for operation in migration.operations:

                        self.stdout.write("    - %s\n" % operation.describe())

                # Write it

                if not self.dry_run:

                    migrations_directory = os.path.dirname(writer.path)

                    if not directory_created.get(app_label, False):

                        if not os.path.isdir(migrations_directory):