[1.2.X] Fixed #13599 -- No longer embed hidden `<td>` elements in `ChangeList`...

[1.2.X] Fixed #13599 -- No longer embed hidden `<td>` elements in `ChangeList` that cause improper rendering when `list_editable` is enabled; refactored `admin_changelist` tests.  Thanks, skevy for bug report and patch.

Backport of r13744 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@13745 bcc190cf-cafb-0310-a4f2-bffc1f526a37