Fix for appended lists (to avoid TypeError exceptions)

When using a recent version of autopkg it was immediately giving exceptions on the lines in the pull request.

```
Traceback (most recent call last):
  File "Code/autopkg", line 1180, in <module>
    sys.exit(main(sys.argv))
  File "Code/autopkg", line 1174, in main
    exit(subcommands[verb]['function'](argv))
  File "Code/autopkg", line 979, in run_recipes
    recipe = load_recipe(recipe_path, override_dirs, search_dirs)
  File "Code/autopkg", line 231, in load_recipe
    name, override_dirs + recipe_dirs)
TypeError: can only concatenate list (not "NSCFArray") to list
```