Fix r_g_q_results_formatter_factory() to produce the result advertised in 130fa835

If reader *or* writer is requested and the format in question supports both
return the formatter factory.

(rasqal_get_query_results_formatter_factory): query reader and writer flags
individually instead of insisting on total equality
Merge pull request #2 from hroptatyr/fix/formats_check

Fix r_g_q_results_formatter_factory() to produce the result advertised in 130fa83