Accept views argument that is an array of values

I read that CCK is frozen in 5.x, and I don't expect this feature to get in, but I'm submitting the idea and documenting it.

I'm using a Node Reference argument handler. Because of the complicated relationship of my data, I want to find not just a single node, but one of potentially many nodes. So my custom argument handling code returns an array of node-ids, instead of a single nid.

  $nids = array(/* lots of node-ids in here */);
  return array(0 => $nids)

instead of

  return array(0 => $nid);

The problem is that content_views_argument_handler() assumes that $arg is a single value and not an array. This simple patch checks if $arg is an array, and if it is, uses a SQL IN clause instead of a simple comparison.

I don't know what other use cases this has, but it seems like there would be many.