Address multi-valued fields in search response.

Fixes #464
Modified search itest for field multivalue.

The itest confirms the fix works by indexing a JSON object with
"multi_ss" : ["this", "that"] and going a search for multi_ss:t*

The returned response contains both this and that mapped to the
"multi_ss" key
Merge pull request #471 from basho/gh464-search-fields

Address multi-valued fields in search response.