Fd's cache does not handle changes in the state of its IOHandle parameter.
If we allow:
Fd f;
f->close();
then Fd ends up caching a pointer to a closed Fd, and will become very
badly confused if a new Fd appears with the same int identifier.
Fix by removing the close method.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
Rewrite Fd using a much simpler named resource template class with
a more straightforward derivation strategy.
Behavior change: we no longer throw an exception while calling get_fd()
on a closed Fd. This does not seem to bother any current callers except
for the tests.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
