Gio::Application: Destructor: Use noexcept in the implementation too.

Bug #566426 (https://bugs.gentoo.org/show_bug.cgi?id=566426)

--- a/gio/giomm/application.cc	2015-09-22 11:13:25.000000000 +0200
+++ b/gio/giomm/application.cc	2015-12-08 21:54:44.914338546 +0100
@@ -284,7 +284,7 @@ Application::Application(const Glib::ust
 
 }
 
-Application::~Application()
+Application::~Application() noexcept
 {
   // Delete all OptionArgCallbackData instances that belong to this application.
   Glib::Threads::Mutex::Lock lock(option_arg_callback_data_mutex);