Fixed #2986 -- Made the JavaScript code that drives related model instance addition in a popup window handle a model representation containing new lines. Also, moved the escapejs functionality yoo django.utils.html so it can be used from Python code. Thanks andrewwatts for the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15131 bcc190cf-cafb-0310-a4f2-bffc1f526a37