MFC r226403:

MFC r226403:

In r225809 the intention was to send VEOF only once if STDIN was not a
terminal. Unfortunately the fix was incorrect and for flushtime > 0 it
keept sending VEOF.

Sent VEOF generates ^D\b\b echoed by the terminal, which was reported
in bin/161526. Note, we still send VEOF at least once. Otherwise
commands like below would hang forever:

  echo 1 |script /tmp/script.out cat

PR:		bin/161526
Reported by:	Adrian Wontroba <aw1@stade.co.uk>, Stefan Bethke <stb@lassitu.de>
Tested by:	Stefan Bethke <stb@lassitu.de>

git-svn-id: svn://svn.freebsd.org/base/stable/8@226592 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f