pty: Use FD_CLOEXEC when opening the PTY master
pty: Use FD_CLOEXEC when opening the PTY master

https://bugzilla.gnome.org/show_bug.cgi?id=747046

thestinger/vte-ng,thestinger/vte-ng,thestinger/vte-ng,saitoha/vte-sixel,saitoha/vte-sixel,saitoha/vte-sixel