doing a little cleanup on the visitors

lib/arel/visitors/dot.rb

@@ -1,6 +1,6 @@
 module Arel
   module Visitors
-    class Dot
+    class Dot < Arel::Visitors::Visitor
       class Node # :nodoc:
         attr_accessor :name, :id, :fields
 
@@ -23,7 +23,7 @@ module Arel
       end
 
       def accept object
-        visit object
+        super
         to_dot
       end
 
@@ -188,7 +188,7 @@ module Arel
         @seen[node.id] = node
         @nodes << node
         with_node node do
-          send "visit_#{o.class.name.gsub('::', '_')}", o
+          super
         end
       end
 

lib/arel/visitors/join_sql.rb

@@ -9,6 +9,8 @@ module Arel
     # This visitor is used in SelectManager#join_sql and is for backwards
     # compatibility with Arel V1.0
     class JoinSql < Arel::Visitors::ToSql
+      private
+
       def visit_Arel_Nodes_SelectCore o
         [o.froms].grep(Nodes::Join).map { |x| visit x }.join ', '
       end

lib/arel/visitors/mysql.rb

@@ -1,6 +1,8 @@
 module Arel
   module Visitors
     class MySQL < Arel::Visitors::ToSql
+      private
+
       def visit_Arel_Nodes_UpdateStatement o
         [
           "UPDATE #{visit o.relation}",

lib/arel/visitors/order_clauses.rb

@@ -1,6 +1,8 @@
 module Arel
   module Visitors
     class OrderClauses < Arel::Visitors::ToSql
+      private
+
       def visit_Arel_Nodes_SelectStatement o
         o.orders.map { |x| visit x }
       end