Fix build with newer (0.28+) vala versions, from:
http://www.linuxquestions.org/questions/slackware-14/midori-compile-fail-ambiguous-reference-between-glib-and-gtk-4175542325/

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>

diff -Nura midori-0.5.9.orig/extensions/history-list.vala midori-0.5.9/extensions/history-list.vala
--- midori-0.5.9.orig/extensions/history-list.vala	2015-07-03 21:05:01.183360199 -0300
+++ midori-0.5.9/extensions/history-list.vala	2015-07-03 21:05:48.959900926 -0300
@@ -319,7 +319,7 @@
         }
 
         private void create_widgets () {
-            ListStore model;
+            Gtk.ListStore model;
             TreeIter iter;
             TreeIter? active_iter = null;
 
@@ -331,7 +331,7 @@
 
             var tab_closing_behavior = this.hl_manager.get_integer ("TabClosingBehavior");
 
-            model = new ListStore (2, typeof (string), typeof (int));
+            model = new Gtk.ListStore (2, typeof (string), typeof (int));
 
             model.append (out iter);
             model.set (iter, TabClosingBehaviorModel.TEXT, _("Do nothing"),