Exception#cause

* NEWS (Core classes updates): add Exception#cause.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43638 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2013-11-11

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43639 b2dd03c8-39d4-4d8f-98ff-823fe69b080e