Un-hardcode the use of LeftJoin. Make it dependent on the presence of a left_join_list parameter to the catalog that lists the names of virtual_columns whose related table definitions should be left-joined, insteand of inner-joined, to the catalog.

git-svn-id: https://svn.erp5.org/repos/public/erp5/sandbox/catalog_join@42277 20353a03-c40f-0410-a6d1-a30d3c3de9de