[1.2.X] Fixed #11223 -- Fixed logout view to use the 'next' GET parameter...

[1.2.X] Fixed #11223 -- Fixed logout view to use the 'next' GET parameter correctly as described in the docs, while only allowing redirection to the same host.

Backport from trunk (r15706).

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15707 bcc190cf-cafb-0310-a4f2-bffc1f526a37