Change get_url to generate URL with trailing splash.

URLField in django by default force to store url with trailing splash in the end.
Let's generate url with tailing splash that after save or update value is not changed.

To avoid problems like this:

```AssertionError: u'http://www.BskxixnfuHpzmpjKTsuoSCdNBHdOdV.com' != u'http://www.BskxixnfuHpzmpjKTsuoSCdNBHdOdV.com/'```
Merge pull request #187 from yrik/patch-1

Change get_url to generate URL with trailing splash.