h5dump doesn't display UTF-8 attributes correctly

I store variable-length UTF8 strings in attributes. Sometimes this includes non-ASCII characters. When I examine the attributes using `h5dump -A`, the single character `Ξ` becomes the 18 characters `\37777777716\37777777636`. This is inconvenient, particularly because my terminal (and all modern ones) supports UTF8 and is perfectly capable of displaying `Ξ`.

It would be convenient if `h5dump` were able to output the UTF8 and let my terminal display it, either as default behaviour or as an option.