merge revision(s) 44630,44631: [Backport #9403]

	* lib/delegate.rb (Delegator): keep source information methods
	  which start and end with '__'.  [ruby-core:58572] [Bug #9155]
	  which start and end with '__'.  [ruby-core:59718] [Bug #9403]


git-svn-id: svn+ssh://svn.ruby-lang.org/ruby/branches/ruby_2_1@44794 b2dd03c8-39d4-4d8f-98ff-823fe69b080e