Bug#829591: hurd: pseudoterminal hangs when I press ^O (flush)

[Kalle Olavi Niemitalo <kon@iki.fi>]

I patched term/users.c (open_hook) so it clears the FLUSH_OUTPUT
flag if the tty was not already open.

I built hurd from commit bc170131016969f1d79409337833046ae1f4501b
(2016-06-14 "pfinet: fix memory leak") + the following changes:

* debian/patches/exec_filename_*.patch from the Debian hurd
  1:0.8.git20160522-4 sources, for https://savannah.gnu.org/bugs/?28934
* term/users.c change described above
* trans/streamio.c change for https://savannah.gnu.org/bugs/?48371
* libpipe/pipe.c change for https://savannah.gnu.org/bugs/?48372

I installed /hurd/exec, /hurd/exec.static, /hurd/ext2fs,
/hurd/ext2fs.static, /hurd/fifo, /hurd/new-fifo, /hurd/pflocal,
/hurd/streamio, /hurd/term, /lib/i386-gnu/libpipe.a, and
/lib/i386-gnu/libpipe.so.0.3.  Then rebooted.

To test the change, I connected to the Hurd VM via SSH and got
/dev/ttyp0.  Then ran cat, typed abc, pressed ^O, typed def
(which did not appear), killed the ssh client, and connected
again.  The motd and the shell prompt appeared OK, and the tty
command showed that this was /dev/ttyp0 again.

I also built vim-7.4.1829 and ran its test suite, which passed.