[1.2.X] Fixed #11376: added some extra tests for autoescaping subtleties.

Thanks, Stephen Kelly.

Backport of [13461] from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@13463 bcc190cf-cafb-0310-a4f2-bffc1f526a37