make Topic/more consistency more consistent

made Jena and sesame sparql updates more consistent. Also fixed a few things along the way. 
This is purposeful in this case. The most common use case would be to have your GraphSparqlEngine run in the same thread - that-s why belove you initially used an immediate future. And that makes sense. If we pick up the default EC then we're likely to do the complicated thing that people don't really want.