Fix comment edit redirect

This fixes #609.

There is really not much to say about this. `ret_url` is still not very nice. And if you use the edit links `href` directly (e.g. by opening in a new tab explicitly) the `ret_url` will bring you to the `.overlay` page without navigation and such. I believe those are intrinsic problems in the stuff we did for #535. Not nice, but still better than before.