[1.2.X] Fixed #13351: Added documentation about the cx_Oracle 'threaded'...

[1.2.X] Fixed #13351: Added documentation about the cx_Oracle 'threaded' option to the oracle backend notes.

Backport of r14630 from trunk.

Thanks to Skaffen for the suggestion.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@14632 bcc190cf-cafb-0310-a4f2-bffc1f526a37