[cluttermm] test-actors: show() still seems to be necessary on the stage.

[Murray Cumming <murrayc src gnome org>]

commit 6ab55ac633ca9401217cc6252477532880bd8024
Author: Murray Cumming <murrayc murrayc com>
Date:   Wed Mar 26 21:27:26 2014 +0100

    test-actors: show() still seems to be necessary on the stage.
    
    But I still don't see anything else.

 examples/test-actors.cc |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/examples/test-actors.cc b/examples/test-actors.cc
index 2df62a4..36eda52 100644
--- a/examples/test-actors.cc
+++ b/examples/test-actors.cc
@@ -222,6 +222,8 @@ int main(int argc, char *argv[])
   // Add the group to the stage
   stage->add_child(oh.group);
 
+  stage->show();
+
   stage->signal_button_press_event().connect(sigc::bind(sigc::ptr_fun
       (on_button_press), stage));