The relation_migrate submodule is not compatible with latest Migrate 2.8

What does it need to make relation_migrate compatible with Migrate 7.x-2.8? Where are the incompatibilities? I currently need to add relations (between two nodes and between a field-collection and a node) by a custom migration.

I used this tutorial to get migration for relation to work. I copied the destination handler (relation_migrate.destination.inc) in a custom module, to don't conflict on relation upgrades and modified it. Basically I removed 'not null' => TRUE, from getKeySchema(), and added following to fields: fields().

    $fields['entity_id_source'] = t('Relation: Entity ID Source');
    $fields['entity_id_destination'] = t('Relation: Entity ID Destination');

I added the patch for that, but currently I am to busy to test it. But let's see if it works.

I also added my Migration class (uses Drupal-to-Drupal data migration) to show how I have implemented the handler. In the child classes I only have to refine the the query and in hook_migrate_api() I added the relation like that:

function custom_migrate_migrate_api() {

    // ...

    'RelationXxxToYyy' => array(
      'class_name' => 'CustomRelationXxxToYyyMigration',
      'description' => t('Migration of relations between Xxx and Yyy.'),
      'destination_type' => 'relation_xxx_to_yyy',
      'endpoint_source_type' => 'node',
      'endpoint_destination_type' => 'node',
      'relation_source_migration'  => 'Xxx',
      'relation_destination_migration' => 'Yyy',
      'relation_table' => 'tabble_xxx_to_yyy',
      'relation_table_source_id' => 'id_xxx',
      'relation_table_destination_id' => 'id_yyy',
      'dependencies' => array('Xxx', 'Yyy'),
    ),

    // ...

That way different relation migrations could be defined without much coding.

Added relation-base.inc.txt, as relation-base.inc was not uploaded in #16.