Added savepoint support to the Oracle backend, necessary per the thread at...

Added savepoint support to the Oracle backend, necessary per the thread at http://groups.google.com/group/django-developers/browse_thread/thread/c87cf2d97478c068/

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10022 bcc190cf-cafb-0310-a4f2-bffc1f526a37