Merge pull request #1462 from jeremyevans/sessionid-to_s

Make SessionId#to_s be an alias of #public_id

lib/rack/session/abstract/id.rb

@@ -29,9 +29,9 @@ def private_id
       end
 
       alias :cookie_value :public_id
+      alias :to_s :public_id
 
       def empty?; false; end
-      def to_s; raise; end
       def inspect; public_id.inspect; end
 
       private