[BUGFIX] setParentRoles() fails if passed roles contain duplicates
Fixes an issue where Doctrine failed inserting parent roles if the array
passed to Role->setParentRoles() contained duplicates.
Even though getParentRoles() does return roles without duplicates,
setParentRoles() did not filter duplicates and caused the SQL error
mentioned in the related issue ticket.
Releases: master, 2.0