Add lazy reification method to ActiveFedora::SolrService

Added ActiveFedora::SolrService.lazy_reify_solr_results to provide lazy (Ruby 1.9-compatible) reification alternative to .reify_solr_results. (Unfortunately, we can't yet use Ruby 2.0's Enumerable#lazy.)
ActiveFedora::SolrService.reify_solr_results refactored, extracting single reification to .reify_solr_result.
Supplied missing test for :load_from_solr option to .reify_solr_results.