Record dependency on Emacs 24.3 and update commentary.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43477 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2013-10-31

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43478 b2dd03c8-39d4-4d8f-98ff-823fe69b080e