Bug#800798: gtk+3.0: Please add breaks for python(3)-gi << 3.18

[Christoph Reiter]

Source: gtk+3.0
Severity: normal

Dear Maintainer,

GTK+ 3.18 breaks some things [0] in combination with older pygobject (python-
gi, python3-gi in debian) which are fixed in pygobject 3.18.

For example this causes: https://bugs.debian.org/cgi-
bin/bugreport.cgi?bug=800795

I'm not sure if this is the right thing to do but maybe add a breaks << 3.18
for the two packages in gir1.2-gtk-3.0?

[0] https://bugzilla.gnome.org/show_bug.cgi?id=749625



-- System Information:
Debian Release: stretch/sid
  APT prefers unstable
  APT policy: (900, 'unstable'), (900, 'testing'), (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.1.0-2-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_US.utf8, LC_CTYPE=en_US.utf8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)