adding attribute#lower for lowercasing an attribute

lib/arel/attributes/attribute.rb

@@ -4,6 +4,12 @@ class Attribute < Struct.new :relation, :name
       include Arel::Expressions
       include Arel::Predications
       include Arel::Math
+
+      ###
+      # Create a node for lowering this attribute
+      def lower
+        relation.lower self
+      end
     end
 
     class String    < Attribute; end

test/test_attributes.rb

@@ -2,6 +2,14 @@
 
 module Arel
   describe 'Attributes' do
+    it 'responds to lower' do
+      relation  = Table.new(:users)
+      attribute = relation[:foo]
+      node      = attribute.lower
+      assert_equal 'LOWER', node.name
+      assert_equal [attribute], node.expressions
+    end
+
     describe 'for' do
       it 'deals with unknown column types' do
         column = Struct.new(:type).new :crazy