i9e: Restore file status flags on exit.

The i9e subsystem sets the stdin and stdout fds passed to i9e_open()
to nonblocking mode but misses to restore the original flags in
i9e_close(). This causes terminal applications like dialog to fail
if they are started in the same terminal after e.g. para_play was
executed.

This commit modifies i9e_open() to fetch and save the file status
flags before setting the O_NONBLOCK flag, and i9e_close() to restore
the original value. STDERR is not affected.