[1.2.X] Fixed #14355 -- Ensure that help_text is displayed for readonly fields...

[1.2.X] Fixed #14355 -- Ensure that help_text is displayed for readonly fields in the admin. Thanks to jester for the report, and to alexbmeng, subsume, wamberg and Julien Phalip for ther work on the patch.

Backport of r15582 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15583 bcc190cf-cafb-0310-a4f2-bffc1f526a37