Added note to releases/1.4.txt about contrib.auth user password hash-upgrade...

Added note to releases/1.4.txt about contrib.auth user password hash-upgrade sequence. Thanks, ericholscher

git-svn-id: http://code.djangoproject.com/svn/django/trunk@17687 bcc190cf-cafb-0310-a4f2-bffc1f526a37