Taxonomy <none> option does not get selected, resulting in error

OK, this is a subtle bug. To verify:

1. You have to have at least two vocabs (Voc1 and Voc2) with multiple term selection enabled, with "not required" option.
2. Go to a node, select a term (call it Term1) for Voc1, and "none" for Voc2.
3. Save.
4. Go back to edit.
5. *bug* - the "none" option is not highlighted (nothing is selected for Voc2).
6. Do changes to your nodes, save, get error: "Illegal choice for Voc2".

Now, why doesn't the "none" option in vocab get selected? The problem is in _taxonomy_term_select($title, $name, $value, $vocabulary_id ... ) function that gets called for every vocab. However, $value array contains terms for ALL vocabs. In our case, $value has Term1 for Voc1, but the form is creating select options for Voc2. Term1 is not in Voc2, but the logic in the code does not catch such cases.

My patch is very minimal, it does additional check for cases where terms belong to other vocabularies, and sets the default option. In general, the relevant code logic in taxonomy.module is confusing -- I would think that a better solution would be to filter only terms that belong to a specific vocabulary in the calling function before creating a form for that vocabulary.

Darius