Description copied from https://bugzilla.gnome.org/show_bug.cgi?id=772354#c19.

Recent commit d4e25a5 causes GNOME Terminal to leak a pts when a tab is closed. After using it for several days, I have 4 tabs but with hundreds of pts in /dev/pts.

Steps to Reproduce:
1. Start terminal with 3 tabs and type 'tty' command in each tab. My result is /dev/pts/25, /dev/pts/26, /dev/pts/27.
2. Close the first tab (/dev/pts/25) and we have 2 tabs left in this step.
3. Open a new tab. We have 3 tabs again in this step.

Expected Results:
The newly opened tab should reuse the recently closed pts (/dev/pts/25).

Actual Results:
The newly opened tab use /dev/pts/28, and /dev/pts/25 still exists. On FreeBSD, you can run 'procstat -f <pid>' and see 4 pts are opened by gnome-terminal-server. The same problem also happens on Linux, but I don't know which command can be used to show the name of opened pts. 'lsof -p <pid>' and 'ls -l /proc/<pid>/fd' only show /dev/ptmx.

$ procstat -f 33650
  PID COMM                FD T V FLAGS    REF  OFFSET PRO NAME
33650 gnome-terminal-serv  text v r r-------   -       - -   /home/lantw44/gnome/devinstall/libexec/gnome-terminal-server
33650 gnome-terminal-serv   cwd v d r-------   -       - -   /home/lantw44
33650 gnome-terminal-serv  root v d r-------   -       - -   /
...
33650 gnome-terminal-serv    23 t - rw---n--   1       0 -   pts/25
33650 gnome-terminal-serv    24 t - rw---n--   1       0 -   pts/26
33650 gnome-terminal-serv    25 t - rw---n--   1       0 -   pts/27
33650 gnome-terminal-serv    26 t - rw---n--   1       0 -   pts/28