Update gtkmm Visual Studio Projects

* MSVC_Net2005/gtkmm/gtkmm.vcproj:
  MSVC_Net2008/gtkmm/gtkmm.vcproj:
  MSVC_Net2010/gtkmm/gtkmm.vcxproj:
  MSVC_Net2010/gtkmm/gtkmm.vcxproj.filters: Add the newly-added sources
  in the gtkmm project files so that gtkmm can be correctly built.