GtkActionBar properties removed

[Juan Rafael García Blanco <juanrgar gmail com>]

Hi,

Before gtkmm tag 3.11.5, Gtk::ActionBar was incorporated to gtkmm. It contained two properties: spacing and 
venter-widget. At that time, those two properties were present in GtkActionBar; however, 10 days ago, those 
two properties gone away. Can these two properties be removed from Gtk::ActionBar too? gtkmm 3.11.5 tarballs 
contain these two properties.

Thank you very much.

Best regards,
Juan.