func NewReader(c context.Context, blobKey appengine.BlobKey) Reader {
	return openBlob(c, blobKey)
}
func NewReader(c context.Context, blobKey appengine.BlobKey) Reader {
	return openBlob(c, blobKey)
}
// NewReader returns a reader for a blob. It always succeeds; if the blob does
// not exist then an error will be reported upon first read.