`open-input-file' in (rnrs io simple) can not recognize UTF-8 encoded file,
`open-input-file' in core do not have this problem.

I think it is caused by a bug in definition of `open-input-file', which
forget to pass third argument `buffer-mode' to `open-file-input-port'.

BTW, `open-output-file' seems to have a similar problem.