Updated the regex to prevent it from turning some.organization, an.inter...

...n etc. into urls. Added a test to make sure this is not happening.

Changes made per this request: [request]
New changes should match foo.com foo.com/bar but not foo.commercial.

[request]:https://github.com/django/django/commit/a93ee5112d42d37187e30aa4edcc1864a79d384a#commitcomment-6888030