slightly more automated proof of [irput_ok]
slightly more automated proof of [irput_ok]

also annotate the [autorewrite with core] that is still needed because
of coq bug 4197.

mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl