Fix Feeds integration.

Thanks for having Feeds integration, that's awesome.

The problem is that weight_feeds_set_target() makes assumptions about how values are returned that are incorrect. Currently, $value could be singular or an array. Every Feeds target callback checks for this. That's dumb, I know. We're trying to fix it in, #2093651: Simplify target callbacks..

A backwards compatible solution is provided, as well as some validation. I'm making some assumptions about your module, since I am not very familiar with it.