Show only 10 characters of the SecureRandom hex value in private URLs

Before:

![Screenshot from 2013-02-18 23:56:52](https://f.cloud.github.com/assets/342081/169552/1f5723b8-7a27-11e2-803b-4486642c72c7.png)

After:

![Screenshot from 2013-02-18 23:57:33](https://f.cloud.github.com/assets/342081/169553/2237c880-7a27-11e2-8338-a72d05fc3339.png)