Include "__fpending.h" once again.

Include "__fpending.h" once again.
Include <stdbool.h>.
(close_stdout): Don't fail just because stdout was closed initially,
since some programs don't write to stdout in the normal course of
operation (other than --version and --help), and we don't want this
function to make e.g. `touch file >&-' fail.
But do fail if it was closed and someone has tried to write to it.
E.g., `printf foo >&-' must fail.