(rasqal_query_results_sort): Survive being asked to sort a NULL sequence.
(rasqal_literal_as_uri): Just return NULL when it's not a URI
(manifest_test_print): Handle non-querys
(manifest_test_run): Warn and return if there is no query.
Added rasqal_dataset_triples iterator class

(rasqal_dataset_get_triples_iterator,
rasqal_free_dataset_triples_iterator): Added constructor and
destructor.

(rasqal_dataset_triples_iterator_get,
rasqal_dataset_triples_iterator_next): Added methods to get and move
(rasqal_dataset_print): Added
Handle reading RDF graph results: default to guess and set a base URI
(manifest_test_run): Print expected graph triples using
rasqal_dataset_print() in debug mode.

Do no fail with an actual graph result at results stage.