playing to update package (failed)
I thought to build gnome-todo package 3.19 branch.
Once tried to do that, it seems to need gtk+3.0 (>= 3.19.5), however Debian doesn't have it yet (of course, it's development branch). Then tried to build gtk+3, it needs wayland
Build again, gtk+3.0 needs "wayland-protocols" that has not been packaged in Debian, yet. Okay... (20 min work...) done! Make wayland-protocols package (not ITPed yet since who should be maintainer, under same umbrella as wayland?), not difficult.
Build newest gtk+3.0 source as 3.19.8 with cowbuilder chroot with those package (cowbuilder --login --save-after-exec --inputfile foo.deb --inputfile bar.deb), ...and failed with testsuite ;) I don't have enough knowledge to investigate it.
Back to older gtk+3.0 source, build 3.19.1 is fine (diff), but 3.19.2 was failed to build, 3.19.3 to 3.19.8 were failed with testsuite.
Time is up, "You lose!"... that's one of typical days.