Fixed #4548 -- Added username hint to admin's change_password form.

django/contrib/admin/templates/admin/auth/user/change_password.html

@@ -20,6 +20,7 @@
 {% endif %}
 {% block content %}<div id="content-main">
 <form action="{{ form_url }}" method="post" id="{{ opts.model_name }}_form">{% csrf_token %}{% block form_top %}{% endblock %}
+<input type="text" name="username" value="{{ original.get_username }}" style="display: none" />
 <div>
 {% if is_popup %}<input type="hidden" name="_popup" value="1" />{% endif %}
 {% if form.errors %}