TAB completion doesn't work with Gtk3
When I press 'Ast<TAB>' I get 'Ast\t' instead of the tab completion.
From the discussion on MUC:
[23:14:15] mcepl: Asterix: yes, I suspect it something py3k/Gtk3-related, but I just wondered where should I look for the treatment of TABs.
[23:17:03] Asterix: mcepl: that's maybe the code at the end of message_textview.py that is commented because (IIRC) there was no binding for that when we did the migration ...
[23:17:19] mcepl: I see, I'll take a look