Create a hook for other modules to import/export elements related to taxonomy

This patch only create a specific hook for taxonomy_export: hook_taxonomy_export_process(). There are 4 operations in this hook:

• export vocabulary
• export terms
• import vocabulary
• import term

Exemple of implementation of this hook:

/**
* Implementation of hook_taxonomy_export_process().
* Module taxonomy_export
*/
function mymodule_taxonomy_export_process(&$edit, $op) {
  switch ($op) {

    // $edit -> vocabulary object
    case 'export vocabulary':
      // Some operations with $edit->vid...
      // ...
      $edit->new_attribute = mymodule_get_vid_attribute($edit->vid);
      break;

    // $edit -> array of term objects (tree)
    case 'export terms':
      if (! empty($edit)) {
          foreach ($edit as &$term) {
            $term->my_attribute = mymodule_get_term_attribute($term->tid);
          }
        }
      }
      break;

    // $edit -> vocabulary array
    case 'import vocabulary':
      if (! empty($edit['new_attribute'])) {
        mymodule_save_vid_attribute($edit['vid'], $edit['new_attribute']);
      }
      break;

    // $edit -> term array
    case 'import term':
      // Term data have already been saved because mymodule implements the hook_taxonomy and taxonomy_save_term()
      // has been called by taxonomy_export_module before invocate this hook. So there is nothing to do.

      // But I can do anything I want here with the $edit array if I really need!
      break;
  }
}

I need this patch to import/export term fields definitions and data for term_fields module within your module. I will not commit any new release of term_fields module before you agree with my patch, so there is no implementation of this hook in the current code. That's why I wrote above an example of use for the suggested hook.

So I created the patch below which is generic and may work with any module who also needs to use your import/export functionalities.