Fix test failure for ruby 1.8.

BigDecimal.new needs to take a string rather than an integer in ruby 1.8.

activerecord/test/cases/relation/where_test.rb

@@ -52,7 +52,7 @@ def test_where_with_boolean_for_string_column
     end
 
     def test_where_with_decimal_for_string_column
-      count = Post.where(:title => BigDecimal.new(0)).count
+      count = Post.where(:title => BigDecimal.new('0')).count
       assert_equal 0, count
     end