Content relations can't be deleted from the "other end" #156

If you try to remove a content relation from the end it wasn't created originally this doesn't work.

The problem seems to be in Mlp_Content_Relations.php->delete_relation. The where-clause doesn't consider this situation.

I'll continue playing around to see if coming from the wrong side also is an issue with other things like changing a relation.

I also wonder if this is an intended limitation or a known issue.