Implement wxNotificationMessage using libnotify in wxGTK.

Use libnotify -- if detected by configure -- to provide native notifications
in wxGTK. Our API maps to libnotify one in rather straightforward way, we
might consider extending it to cover more of libnotify functionality
(categories, user-defined icons and, especially, actions) later.

Also update the dialogs sample to show another kind of notification and the
documentation to clarify the behaviour of various methods.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72218 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk/notifmsg.h

@@ -0,0 +1,47 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        wx/gtk/notifmsg.h
+// Purpose:     wxNotificationMessage for wxGTK.
+// Author:      Vadim Zeitlin
+// Created:     2012-07-25
+// RCS-ID:      $Id$
+// Copyright:   (c) 2012 Vadim Zeitlin <vadim@wxwidgets.org>
+// Licence:     wxWindows licence
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef _WX_GTK_NOTIFMSG_H_
+#define _WX_GTK_NOTIFMSG_H_
+
+typedef struct _NotifyNotification NotifyNotification;
+
+// ----------------------------------------------------------------------------
+// wxNotificationMessage
+// ----------------------------------------------------------------------------
+
+class WXDLLIMPEXP_ADV wxNotificationMessage : public wxNotificationMessageBase
+{
+public:
+    wxNotificationMessage() { Init(); }
+    wxNotificationMessage(const wxString& title,
+                          const wxString& message = wxString(),
+                          wxWindow *parent = NULL,
+                          int flags = wxICON_INFORMATION)
+        : wxNotificationMessageBase(title, message, parent, flags)
+    {
+        Init();
+    }
+
+    virtual ~wxNotificationMessage();
+
+
+    virtual bool Show(int timeout = Timeout_Auto);
+    virtual bool Close();
+
+private:
+    void Init() { m_notification = NULL; }
+
+    NotifyNotification* m_notification;
+
+    wxDECLARE_NO_COPY_CLASS(wxNotificationMessage);
+};
+
+#endif // _WX_GTK_NOTIFMSG_H_