* configure.ac (AC_CHECK_HEADERS): Add sys/select.h and sys/time.h.
* src/estream.c: Include both header if available.
(COOKIE_IOCTL_NONBLOCK): New.
(struct estream_cookie_fd): Add field nonblock.
(func_fd_create): Set nonblock from MODEFLAGS.
(es_func_fd_ioctl): New.
(parse_mode): Add modeflag "nonblock".
(es_fill): Map EWOULDBLOCK to EAGAIN.  Do not set error indicator for
EAGAIN.
(es_flush, es_seek, es_write_nbf): Map EWOULDBLOCK to EAGAIN.
(do_fdopen): Call COOKIE_IOCTL_NONBLOCK.
(_gpgrt_set_nonblock): New.
(_gpgrt_get_nonblock): New.
(_gpgrt_poll): New.
* src/gpg-error.h.in (struct _gpgrt_poll_s): New.
(gpgrt_poll_t, es_poll_t): New.
(es_set_nonblock, es_get_nonblock, es_poll): New.
* src/gpg-error.vers, src/gpg-error.def.in: Add gpgrt_set_nonblock,
gpgrt_get_nonblock, and gpgrt_poll.
* src/visibility.c (gpgrt_set_nonblock, gpgrt_get_nonblock): New.
(gpgrt_poll): New.
* tests/t-common.h (DIM): New.
* tests/t-poll.c: New.
* tests/Makefile.am (TESTS): Add t-poll.
(t_poll_LDADD): New.