1. implemented radio menu items for wxGTK

1. implemented radio menu items for wxGTK
2. changed (in most cases blindly) code for all the others
3. added wx/features.h
4. update wxMenu[Item] docs

----------------------------------------------------------------------
Committing in .

Modified Files:
	distrib/msw/tmake/filelist.txt docs/changes.txt
	docs/latex/wx/menu.tex docs/latex/wx/menuitem.tex
	include/wx/defs.h include/wx/menu.h include/wx/menuitem.h
	include/wx/gtk/menu.h include/wx/gtk/menuitem.h
	include/wx/mac/menuitem.h include/wx/motif/menuitem.h
	include/wx/msw/menuitem.h include/wx/os2/MENUITEM.H
	include/wx/univ/menuitem.h samples/menu/menu.cpp
	src/common/menucmn.cpp src/gtk/menu.cpp src/mac/menuitem.cpp
	src/motif/menuitem.cpp src/msw/menuitem.cpp
	src/os2/MENUITEM.CPP src/univ/menu.cpp
Added Files:
	include/wx/features.h
----------------------------------------------------------------------

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@14674 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775