Don't re-open temporary file.
Don't re-open temporary file.

`Write` is implemented on both `&NamedTemporaryFile` and `&File` so you don't
actually need a mutable reference. I wish there were a better way to do this but
such is life.

matthiasbeyer/imag,matthiasbeyer/imag,mario-kr/imag,mario-kr/imag