Fixed #9136: Do slicing in Oracle with rownum instead of row_number() for a...

Fixed #9136: Do slicing in Oracle with rownum instead of row_number() for a speed improvement. Thanks, Guillaume Taglang.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@9235 bcc190cf-cafb-0310-a4f2-bffc1f526a37