Port nodeconvert.module to Drupal 6

I started on a port to Drupal 6.0 using the codereview (coder) module.

Remaining issues are the following...

node_convert.module

severity: critical Line 133: #multistep is gone, use $form_state instead

$form['#multistep'] = TRUE;

severity: critical Line 250: #multistep is gone, use $form_state instead

$form['#multistep'] = TRUE;

severity: critical Line 377: hook no longer exists, use hook_form_alter() to swap your own validation handler (Drupal Docs)

$db_info_source = content_database_info($field_info_source); // Get DB specific source field information

severity: critical Line 386: hook no longer exists, use hook_form_alter() to swap your own validation handler (Drupal Docs)

$db_info_dest = content_database_info($field_info_dest); // Get DB specific destination field information