Attempt #2 to fix script(1) if the standard input is closed: If we
read EOF from STDIN_FILENO, write zero bytes into the pseudo-terminal;
this is interpreted as an EOF by the program being scripted.

I've tested this with two non-interactive scripts:

1. echo 5 | script foo sh -c 'read x; sleep $x; echo bar'
2. echo bar | xargs script foo echo

and one interactive program:

script foo more /etc/passwd

and everything seems to work properly...

PR: bin/56166, bin/57414, ports/57415, ports/60534
Approved by: rwatson (mentor)
MFC after: 2 weeks