[1.2.X] Fixed #13092 -- Added support for the "in" operator when dealing with...

[1.2.X] Fixed #13092 -- Added support for the "in" operator when dealing with context lists. Thanks to clelland for the patch.

Backport of [13510] from trunk.  Backported in order to support some other
tests which need to be backported.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@13986 bcc190cf-cafb-0310-a4f2-bffc1f526a37