Added Solutions#- and Solution#disjoint? for SPARQL result set negation (minus operator).
* Solution#disjoint? indicates if two solutions overlap or not.
* Solutions#- filters self by removing any solution from another result set which compatible and not disjoint.
Change Solutions#- to Solutions#minus to avoid confusion with normal Array#- behavior.
Added accessor for RDF.value
Define all RDF terms so that #respond_to? will report properly.
Optimize Array casting.
Finish RSpec2.14Update