NTriplesParser.hs: minor cleanup and refactoring of parsing combinators.
NTriplesParser.hs: minor cleanup and refactoring of parsing combinators.

darcs-hash:20071112071253-db1bb-c9cb79f872fece49470411440b2a95697c840dc2

cordawyn/rdf4h,jutaro/rdf4h,LeifW/rdf4h,ddssff/rdf4h