Fixed #18872 -- Added prefix to FormMixin

Thanks @ibustama for the initial patch and dragonsnaker for opening the
report.

docs/ref/class-based-views/mixins-editing.txt

@@ -35,6 +35,10 @@ FormMixin
 
         The URL to redirect to when the form is successfully processed.
 
+    .. attribute:: prefix
+
+        Sets the :attr:`~django.forms.Form.prefix` for the generated form.
+
     .. method:: get_initial()
 
         Retrieve initial data for the form. By default, returns a copy of

docs/releases/1.6.txt

@@ -731,6 +731,9 @@ Miscellaneous
   of the admin views. You should update your custom templates if they use the
   previous parameter name.
 
+* Added :attr:`~django.views.generic.edit.FormMixin.prefix` to allow you to
+  customize the prefix on the form.
+
 Features deprecated in 1.6
 ==========================