Related_name='+' shouldn't clash with another '+'
|Reported by:||akaariai||Owned by:||nobody|
|Component:||Database layer (models, ORM)||Version:||master|
|Has patch:||no||Needs documentation:|
|Needs tests:||Patch needs improvement:|
A relation (fk or m2m) that defines its related name as '+' shouldn't cause a model validation error if there is another relation for the same model with '+'.