AnyRsetView: Refactor the columns_name method and update doc. We drop the 'label_column_%s' % colidx pattern and add a clean column_label method that might be overwritten by children class to alter the way default columns headers are computed.

if repo.system_source.dbdriver == 'postgres':
    sql('ALTER TABLE appears ADD COLUMN weight float')
    sql('UPDATE appears SET weight=1.0 ')