Import multiple values to tag vocabulary

I worked out why this wasn't working - it's a bug.

The attached patch fixes it by merging the existing value (if any) with the new value(s). It was previously ignoring the existing value and overwriting it.
Let me know if this patch fixes it for you too.

Would the same thing apply for taxonomy.inc?

For example, using a free tagging - multitag 'Categories' vocabulary:

Source -> Target:
------------------
Category Level 1 -> Categories
Category Level 2 -> Categories
Category Level 3 -> Categories

The result is, only Level 3 is stored in Categories, 1 & 2 are lost.

In mappers/taxonomy inc, I think this is the solution, change:

  if ($vocab->tags) {
    // Simply add a comma separated list to the node for a "tags" vocabulary.
    $node->taxonomy['tags'][$vocab->vid] = implode(',', $terms);
  }

to this:

  if ($vocab->tags) {
    // Simply add a comma separated list to the node for a "tags" vocabulary.
    $terms = array_merge($terms, explode(',', $node->taxonomy['tags'][$vocab->vid]));
    $node->taxonomy['tags'][$vocab->vid] = implode(',', $terms);
  }

I still need to test this.

I tested the patches (mine attached now), and they really work.

My patch is for 6x10-beta4, but it should apply to latest dev.

If the maintainers feel they should be part of feeds, please include them.

On a side not, my patch might need array_unique to reduce duplicates,

$terms = array_unique(array_merge($terms, explode(',', $node->taxonomy['tags'][$vocab->vid]));

Unless Drupal does this anyway.