add bind values to the manager class

lib/arel/tree_manager.rb

@@ -4,9 +4,12 @@ class TreeManager
 
     attr_reader :ast, :engine
 
+    attr_accessor :bind_values
+
     def initialize engine
       @engine = engine
       @ctx    = nil
+      @bind_values = []
     end
 
     def to_dot

test/test_select_manager.rb

@@ -9,6 +9,13 @@ def test_join_sources
       assert_equal "SELECT FROM 'foo'", manager.to_sql
     end
 
+    def test_manager_stores_bind_values
+      manager = Arel::SelectManager.new Table.engine
+      assert_equal [], manager.bind_values
+      manager.bind_values = [1]
+      assert_equal [1], manager.bind_values
+    end
+
     describe 'backwards compatibility' do
       describe 'project' do
         it 'accepts symbols as sql literals' do