Fixed #11082 -- Ensured that subqueries used in an exclude(X__in=) clause...

Fixed #11082 -- Ensured that subqueries used in an exclude(X__in=) clause aren't pre-evaluated. Thanks to Henry Andrews for the report, and clement for the fix.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10929 bcc190cf-cafb-0310-a4f2-bffc1f526a37