Remove dead links to the Gmane web interface.
The mail to news interface and mail archive "Gmane" went down 2016 and is
only partially restored. http://home.gmane.org/2016/08/29/next-steps-gmane/
Remove dead links to the web interface and add links to the
mail archives at Sourceforge.
TODO: There are still dead links to specific messags in
Bugs.txt, todo.txt and alternatives.txt
Thanks to Luke Plant for reporting the issue.
git-svn-id: http://svn.code.sf.net/p/docutils/code/trunk@8103 929543f6-e4f2-0310-98a6-ba3bd3dd1d04