Fixed Oracle backend not to use extra_select for limit/offset type queries,...

Fixed Oracle backend not to use extra_select for limit/offset type queries, which fixes a majority of the currently failing tests.  Thanks, Ramiro Morales.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@8445 bcc190cf-cafb-0310-a4f2-bffc1f526a37