The term_node table needs vid in D6

Issue Summary

There is a bug in the content importing functionality. On the field mapping page for node imports, under Taxonomy terms (fields), only the following fields are allowed:

Node ID (mapping)
Term ID (mapping)
Title (mapping)
Term name (mapping)

In D6 nodes are (apparently) tagged on a per-revision basis, so the vid is a part of the term_node table's primary key and needs a field mapping. Without it, node terms are not imported properly; the first term for a given node is entered in the table with a 0 for the revision ID (and therefore not actually associated with the node); while subsequent terms for the node are not added at all because of key duplication.