Change implementation of hook_nodeapi()

hook_xmlsitemap_links() should be changed, and do the task of grabbing the taxonomy terms from the Drupal core tables.
This is required because the actual implementation of hook_nodeapi() doesn't work on Drupal 6 when terms of a tags vocabulary are added to the node; in that case, the array containing the terms passed is not on the form [tid] => [term], but it's in the form "tags" => [string] (where [string] is the concatenation of all the terms, separated by a comma).

This is an issue only for the Drupal 6 branch, as the Drupal 5 branch doesn't seem affected by this (probably the tags vocabulary terms are handled differently in Drupal 6).