Add the new button in the addon dialog to the definition as well.

data/gui/default/window/addon.cfg

@@ -121,15 +121,29 @@
 							grow_factor = 0
 
 							[column]
-								grow_factor = 1
+								border = "all"
+								border_size = 5
+								horizontal_alignment = "left"
 
-								[spacer]
+								[button]
+									# just show how the default looks.
 									definition = "default"
-								[/spacer]
+
+									tooltip = "Update locally installed addons."
+
+									size_text = _ "Update add-ons"
+									label = _ "Update add-ons"
+
+									# we define the return value manually instead of being
+									# linked to the id. Not sure whether that's the best
+									# solution, but it's nice as proof-of-concept.
+									return_value = 3
+								[/button]
 
 							[/column]
 
 							[column]
+								grow_factor = 1
 
 								[spacer]
 									definition = "default"

src/addon_management.cpp

@@ -1129,7 +1129,7 @@ namespace {
 
 	const int addon_download  = 0;
 	const int addon_uninstall = 2;  // NOTE this value is also known by WML so don't change it.
-	const int addon_update    = 3;
+	const int addon_update    = 3;  // NOTE this value is also known by WML so don't change it.
 
 } // end unnamed namespace 4
 
@@ -1149,8 +1149,8 @@ void manage_addons(game_display& disp)
 		res = addon_dlg.get_retval();
 		if(res == gui2::twindow::OK) {
 			res = 0;
-			remote_host = addon_dlg.host_name();
 		}
+		remote_host = addon_dlg.host_name();
 	} else {
 		gui::dialog svr_dialog(disp,
 		                       _("Connect to add-ons server"),

src/gui/dialogs/addon_connect.cpp

@@ -40,6 +40,8 @@ namespace gui2 {
  * @start_table = container
  *     [] (button) (2)                 This button closes the dialog and starts
  *                                     the addon manager.
+ *     [] (button) (3)                 This button closes the dialog and starts
+ *                                     the update routine.
  *     host_name (text_box)            This text contains the name of the server
  *                                     to connect to.
  * @end_table