Stringify rendered text unless it's a Proc object for streaming.

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@6560 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

actionpack/lib/action_controller/base.rb

@@ -869,7 +869,7 @@ module ActionController #:nodoc:
           response.body ||= ''
           response.body << text.to_s
         else
-          response.body = text.to_s
+          response.body = text.is_a?(Proc) ? text : text.to_s
         end
       end