[baobab] accelerators: add mouse button 8 for back button

[Stefano Facchini <sfacchini src gnome org>]

commit a69689eaebd96da343f06d44d9459674f8086ece
Author: Gabriel Rauter <rauter gabriel gmail com>
Date:   Thu May 4 15:24:21 2017 +0200

    accelerators: add mouse button 8 for back button
    
    fix bug 771935

 src/baobab-window.vala |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)
---
diff --git a/src/baobab-window.vala b/src/baobab-window.vala
index bbb45c4..5e8f9da 100644
--- a/src/baobab-window.vala
+++ b/src/baobab-window.vala
@@ -185,6 +185,13 @@ namespace Baobab {
 
             set_ui_state (home_page, false);
 
+            button_press_event.connect ( (event) => {
+                if (event.button == 8) {
+                    lookup_action ("show-home-page").activate (null);
+                }
+                return false;
+            });
+
             show ();
         }