hurd: Fix poll and select POSIX compliancy details about errors

hurd: Fix poll and select POSIX compliancy details about errors

This fixes the following:

- On error, poll must not return without polling, including EBADF, and instead
report POLLHUP/POLLERR/POLLNVAL
- Select must report EBADF if some set contains an invalid FD.

The idea is to move error management to after all select calls, in the
poll/select final treatment. The error is instead recorded in a new `error'
field, and a new SELECT_ERROR bit set.

Thanks Svante Signell for the initial version of the patch.

	* hurd/hurdselect.c (SELECT_ERROR): New macro.
	(_hurd_select):
	- Add `error' field to `d' structures array.
	- If a poll descriptor is bogus, set EBADF, but continue with a zero
	timeout.
	- Go through the whole fd_set, not only until _hurd_dtablesize. Return
	EBADF there is any bit set above _hurd_dtablesize.
	- Do not request io_select on bogus descriptors (SELECT_ERROR).
	- On io_select request error, record the error.
	- On io_select bogus reply, use EIO error code.
	- On io_select bogus or error reply, record the error.
	- Do not destroy reply port for bogus FDs.
	- On error, make poll set POLLHUP in the EPIPE case, POLLNVAL in the
	EBADF case, or else POLLERR.
	- On error, make select simulated readiness.