idle_add deprecation warning.

[eugeneai]

I've fixed a deprecation warning for GTK3 backend (GTK-3.9.91).

86cebdc

I could'nt arrange pull request without pulling unnescessary commits. Sorry.

Best regards,
Evgeny

[tacaswell]

create a branch based on current master and then cherry-pick this commit to the new branch. That should give you a clean PR.

[tacaswell]

Closing as this has been idependently fixed in 1b3eee7.