MediaFile: make id3v23 a constructor parameter
MediaFile: make id3v23 a constructor parameter

For #899, we need to change MediaFile's behavior (pre-write) based on whether
we're doing ID3v2.3 or not. So we need a field on the object, not a parameter
to `save()`.

Original: 2e23e8204135353f00917f17b08a8f5344fd9e8a@7de6259

beetbox/mediafile