It's possible to save Friendships with one-self

[zerok]

http://code.google.com/p/django-friends/issues/detail?id=3

Currently, the Friendship model doesn't check to see if from_user is the
same as to_user when saving. This allows the creation of friendships with
oneself.

To fix it, I've added a custom save() method:

def save(self):
    if self.to_user == self.from_user:
        return
    else:
        super(Friendship, self).save()