Fixed #5880 -- Fixed an XSS hole in the admin interface.

 * Escaped text that gets sent after saving the admin foreignkey popup form.
 * Added quotes around the second argument passed to `opener.dismissAddAnotherPopup` to make the function also work when a text field is used as the primary key.
 * Added a `html_unescape` javascript function to unescape the strings passed in to the `dismissAddAnotherPopup` function so that the added choice displays correctly in the dropdown box.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@6691 bcc190cf-cafb-0310-a4f2-bffc1f526a37