Merge pull request #341 from joernhees/master

Dataset.parse() returns ConjunctiveGraph.parse()
Test for issue #336, N3 round-tripping issue for NS localnames. (currently inverted, i.e. asserting failure for the test).
"Fix" for issue #296, GraphValue has no articulated role and no apparent use.
pinning pyparsing to 1.5.7 for Python 2.5