django 1.4 timezone aware datetime support

The current version of django-mailer use datetime.now that returns a naive datetime object. This results in an error with if the new Django time-zone support is enabled (from Django 1.4). This patch solves the issue.

For more information: https://docs.djangoproject.com/en/dev/topics/i18n/timezones/#naive-and-aware-datetime-objects