Fix forN_ok statement to allow any rx
Fix forN_ok statement to allow any rx

Explicit type annotations restricted output to be a prog L, but there
should be no constraint on the return type of the continuation.

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