addbooks --json doesn't support list of authors

[adborden]

I have a books.json created from fetch_ia_item which returns data like

    {
        "a_title": "The wonderful wizard of Oz", 
        "cover_path": "/home/adborden/src/pathagar/static_media/books/wonderfulwizardo00baumiala/wonderfulwizardo00baumiala.gif", 
        "tags": [
            "Adventure and adventurers", 
            "Wizards"
        ], 
        "book_path": "/home/adborden/src/pathagar/static_media/books/wonderfulwizardo00baumiala/wonderfulwizardo00baumiala.epub", 
        "a_summary": "Publisher's green and red illustrated cloth over boards; illustrated endpapers. Plate detached", 
        "a_status": "Published", 
        "a_author": [
            "Baum, L. Frank (Lyman Frank), 1856-1919", 
            "Denslow, W. W. (William Wallace), 1856-1915"
        ]
    }

addbooks imports this as a string: [u'Crane, Thomas, b. 1843?', u'Houghton, Ellen Elizabeth, 1853-1922']