Further improved on the work done in r16622 by making the help text icons look...

Further improved on the work done in r16622 by making the help text icons look hoverable in the admin tabular inline headers.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16690 bcc190cf-cafb-0310-a4f2-bffc1f526a37