Fixed #13349 -- Ensure that raw queries evaluate the entire query if the...

Fixed #13349 -- Ensure that raw queries evaluate the entire query if the backend doesn't support chunked reads. Thanks to Alex Gaynor for the report and patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12978 bcc190cf-cafb-0310-a4f2-bffc1f526a37