merge revision(s) r46391,r46395: [Backport #9766]

	* lib/csv.rb (CSV#<<): honor explicity given encoding.  based on
	  the patch by DAISUKE TANIWAKI <daisuketaniwaki AT gmail.com> at
	  [ruby-core:62113].  [Bug #9766]

	* lib/csv.rb (CSV#<<): honor explicitly given encoding.  based on


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@47586 b2dd03c8-39d4-4d8f-98ff-823fe69b080e