Support multiple feature values per param

[awiner, 2009-06-15 17:17:50]

Addresses a 0.9 compatibility issue, SHINDIG-997:
Features may now have multiple params with the same name

Uses it to support multiple template libraries per gadget, as per spec.

Does not redo the content rewriter feature to be 0.9 compliant, though that
should now be possible.

[levik, 2009-07-01 16:25:30]

Looks great, but does this also pass the new multi-params down to the client? I
didn't notice any code for that - though it's possible that this would happen
automatically...