[1.0.X] Fixed #9706: made SlugField honor max_length in Oracle, matching the...

[1.0.X] Fixed #9706: made SlugField honor max_length in Oracle, matching the other backends. Backport of [9548] from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@9549 bcc190cf-cafb-0310-a4f2-bffc1f526a37