No more mailinglist/alias duplicates

Ghost User
2017-06-28T19:54:40+02:00

Closes #410

#### Previous behaviour
Steps to reproduce:

1. Create a mailing list `mailtest`
2. Make `mailtest2` an alias of `mailtest`
3. Create a mailing list `mailtest2`
4. Observe there is no error while creating the alias ...

Closes #410 (closed)

Previous behaviour

Steps to reproduce:

1. Create a mailing list mailtest

2. Make mailtest2 an alias of mailtest

3. Create a mailing list mailtest2

4. Observe there is no error while creating the alias and lists.

5. Create a mailing list mailtest3

6. Create a mailing list mailtest4

7. Make mailtest3 an alias of mailtest4

8. Observe there is no error while creating the alias and lists.

9. Create a mailing list mailtest5

10. Create another mailing list mailtest5

11. Observe there is no error while creating the lists.

12. Create a mailing list mailtest6

13. Create a mailing list mailtest7

14. Make mailtest8 an alias of mailtest6

15. Make mailtest8 an alias of mailtest7

16. Observe there is no error while creating the aliases.

New behaviour

Steps to validate that it works:

1. Create a mailing list mailtest

2. Make mailtest2 an alias of mailtest

3. Create a mailing list mailtest2

4. Observe there is an error while creating the alias and lists.

5. Create a mailing list mailtest3

6. Create a mailing list mailtest4

7. Make mailtest3 an alias of mailtest4

8. Observe there is an error while creating the alias and lists.

9. Create a mailing list mailtest5

10. Create another mailing list mailtest5

11. Observe there is an error while creating the lists.

12. Create a mailing list mailtest6

13. Create a mailing list mailtest7

14. Make mailtest8 an alias of mailtest6

15. Make mailtest8 an alias of mailtest7

16. Observe there is an error while creating the aliases.