FILE * interfaces

It's great that we made FILE* opaque.

I've run into a (very small) nit in unicon: the language has a poll
interface that looks into the internals of FILE* to figure out
whether there's something in the input buffer before actually calling
poll and the likes. As far as I know, we don't have any interface
(OpenBSD or otherwise) to look inside FILE* to tell us whether
there's still any data to get read (in a non-destructive/non-hanging
manner: meaning: fgetc + ungetc won't work)

This is not life-breaking. But suggestions ?...