Removed: op_code handling for relations
Fixed: version no 1 not recognized as draft
Described removed feature
dbupdate: added queries to cleanup ezcontentboject_link table
Added: ezcontentobject_link cleanup queries for MySQL
Removed: ezcontentobject_link.op_code column
Added: issue number to removed feature description
Removed: dead ezcontentobject_link.op_code usage
Merge pull request #529 from pspanja/EZP-20239

Remove extraneous op_code handling for relations