Add unique constraint to database
Add unique constraint to database
Add checking for used isbns
Reworked handling of used ISBNs
Remove changes to DB, it's all handled in the persitence layer
First try of handling the isbn already used exception in the controller
fix failing tests
Display books with isbn that is already in use on add book form
Add another assertion to make sure the controller loads books with isbn that is already in use
Add explanatoriy msg to jsp
Merge branch '1.6.0_WB127_unique-isbns'