Make OrderedHash#to_a preserve order

lib/mongo/util/ordered_hash.rb

@@ -71,6 +71,11 @@ class OrderedHash < Hash
     end
     alias :each_pair :each
 
+    def to_a
+      @ordered_keys ||= []
+      @ordered_keys.map { |k| [k, self[k]] }      
+    end
+    
     def values
       collect { |k, v| v }
     end

test/test_ordered_hash.rb

@@ -76,6 +76,10 @@ class OrderedHashTest < Test::Unit::TestCase
     assert_equal @ordered_keys, @oh.keys
   end
 
+  def test_to_a_order_preserved
+    assert_equal @ordered_keys, @oh.to_a.map(&:first)
+  end
+
   def test_order_preserved_after_replace
     @oh['a'] = 42
     assert_equal @ordered_keys, @oh.keys