[glibmm] C++11: Use the override keyword.

[Murray Cumming <murrayc src gnome org>]

commit 6638238e1453ecb4334ef10bae2341538e5b6ddf
Author: Murray Cumming <murrayc murrayc com>
Date:   Wed Jul 15 11:43:52 2015 +0200

    C++11: Use the override keyword.

 examples/markup/parser.cc                     |   10 +++++-----
 examples/options/main.cc                      |    7 ++++---
 tests/glibmm_interface_implementation/main.cc |    6 +++---
 3 files changed, 12 insertions(+), 11 deletions(-)
---
diff --git a/examples/markup/parser.cc b/examples/markup/parser.cc
index fafcc2f..b954a67 100644
--- a/examples/markup/parser.cc
+++ b/examples/markup/parser.cc
@@ -54,14 +54,14 @@ public:
   virtual ~DumpParser();
 
 protected:
-  virtual void on_start_element(Glib::Markup::ParseContext& context,
+  void on_start_element(Glib::Markup::ParseContext& context,
                                 const Glib::ustring&        element_name,
-                                const AttributeMap&         attributes);
+                                const AttributeMap&         attributes) override;
 
-  virtual void on_end_element(Glib::Markup::ParseContext& context,
-                              const Glib::ustring& element_name);
+  void on_end_element(Glib::Markup::ParseContext& context,
+                              const Glib::ustring& element_name) override;
 
-  virtual void on_text(Glib::Markup::ParseContext& context, const Glib::ustring& text);
+  void on_text(Glib::Markup::ParseContext& context, const Glib::ustring& text) override;
 
 private:
   int parse_depth_;
diff --git a/examples/options/main.cc b/examples/options/main.cc
index baa3615..d693d09 100644
--- a/examples/options/main.cc
+++ b/examples/options/main.cc
@@ -25,9 +25,10 @@ class ExampleOptionGroup : public Glib::OptionGroup
 public:
   ExampleOptionGroup();
 
-  virtual bool on_pre_parse(Glib::OptionContext& context, Glib::OptionGroup& group);
-  virtual bool on_post_parse(Glib::OptionContext& context, Glib::OptionGroup& group);
-  virtual void on_error(Glib::OptionContext& context, Glib::OptionGroup& group);
+private:
+  bool on_pre_parse(Glib::OptionContext& context, Glib::OptionGroup& group) override;
+  bool on_post_parse(Glib::OptionContext& context, Glib::OptionGroup& group) override;
+  void on_error(Glib::OptionContext& context, Glib::OptionGroup& group) override;
 
   bool on_option_arg_string(const Glib::ustring& option_name,
     const Glib::ustring& value, bool has_value);
diff --git a/tests/glibmm_interface_implementation/main.cc b/tests/glibmm_interface_implementation/main.cc
index ec0ea93..c748215 100644
--- a/tests/glibmm_interface_implementation/main.cc
+++ b/tests/glibmm_interface_implementation/main.cc
@@ -20,9 +20,9 @@ public:
 
 protected:
   //Implement vfuncs:
-  virtual Glib::ustring get_name_vfunc() const;
-  virtual Glib::VariantType get_state_type_vfunc() const;
-  virtual Glib::VariantBase get_state_hint_vfunc() const;
+  Glib::ustring get_name_vfunc() const override;
+  Glib::VariantType get_state_type_vfunc() const override;
+  Glib::VariantBase get_state_hint_vfunc() const override;
 };
 
 CustomAction::CustomAction()