Fix before_type_cast for non-dirty attributes (issue #52).

Only use before_type_cast implementation if earlier than 3.1.0 which has
it's own working version for date/time fields now.

lib/validates_timeliness/attribute_methods.rb

@@ -46,7 +46,7 @@ module ValidatesTimeliness
       def define_timeliness_before_type_cast_method(attr_name)
         method_body, line = <<-EOV, __LINE__ + 1
           def #{attr_name}_before_type_cast
-            _timeliness_raw_value_for('#{attr_name}')
+            _timeliness_raw_value_for('#{attr_name}') || @attributes['#{attr_name}']
           end
         EOV
         generated_timeliness_methods.module_eval(method_body, __FILE__, line)

lib/validates_timeliness/orm/active_record.rb

@@ -7,7 +7,8 @@ module ValidatesTimeliness
         def define_attribute_methods
           super
           # Define write method and before_type_cast method
-          define_timeliness_methods(true)
+          use_before_type_cast = ::ActiveRecord::VERSION::STRING < '3.1.0'
+          define_timeliness_methods(use_before_type_cast)
         end
 
         def timeliness_attribute_timezone_aware?(attr_name)