accept4, dup3, pipe2: port to Cygwin

accept4, dup3, pipe2: port to Cygwin

Problem reported for Emacs by Ken Brown in <http://bugs.gnu.org/14821>.
* lib/accept4.c (accept4) [O_BINARY]:
* lib/dup3.c (dup3) [O_BINARY]:
* lib/pipe2.c (pipe2) [O_BINARY]:
Use set_binary_mode, not setmode.
* lib/pipe2.c [!GNULIB_BINARY_IO]: Include binary-io.h.
* modules/binary-io (Depends-on): Remove module indicator.
These last two bits undo the previous change to pipe2 and binary-io.