A poll of a open file descriptor for /dev/null always returns a POLLERR

under AIX.  This work-around bypasses the eio handling of /dev/null and
instead directly makes pin[0] a file handle for /dev/null.

The only problem with this fix is that it is not obvious elsewhere in the
code that pin is not a pipe when using "srun --batch" and stdin is
/dev/null.