Print all bad apps passed to makemigrations, not just the first one.

        # Make sure the app they asked for exists

        app_labels = set(app_labels)

        bad_app_labels = set()

        for app_label in app_labels:

            try:

                cache.get_app(app_label)

            except ImproperlyConfigured:

                self.stderr.write("The app you specified - '%s' - could not be found. Is it in INSTALLED_APPS?" % app_label)

                bad_app_labels.add(app_label)

        if bad_app_labels:

            for app_label in bad_app_labels:

                self.stderr.write("App '%s' could not be found. Is it in INSTALLED_APPS?" % app_label)

            sys.exit(2)

        # Load the current graph state