Fix LocationError on cyclic dependencies

Fixes #36 

Handle cyclic dependencies properly in ``@manage-upgrades`` view:
- Tell the user that there are cyclic dependencies
- Tell the user which profiles have cyclic dependencies
- Don't let the user upgrade (he can use portal_setup) because he would probably break the site when upgrading on an unsorted profile list.

![bildschirmfoto 2014-01-08 um 09 24 38](https://f.cloud.github.com/assets/7469/1866815/61cda850-783e-11e3-8c1c-152d9584e4a0.png)

4teamwork/ftw.blog#29

@maethu could you review, please?