Fixed #14733: no longer "validate" .raw() queries.

Turns out that a lot more than just SELECT can return data, and this list is
very hard to define up front in a cross-database manner. So let's just assume
that anyone using raw() is at least halfway competant and can deal with
the error messages if they don't use a data-returning query.

Thanks to Christophe Pettus for the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15803 bcc190cf-cafb-0310-a4f2-bffc1f526a37