Following on from
JENA-1029, and the fact RIOT is the default I/O fro apache-jena-libs, the old RDFWriterFImpl, RDFReaderFImpl can be rewritten to work on core fixed set of syntaxes by naming classes, not doing an unnecessary Class.forLoad.
RIOT can wire in as a indirection to RDFReaderFImpl/RDFWriterFImpl, not replace existing registrations. This means adapter code in RIOt is simplified and some can be removed.
Maintain, pedantically, compatibility with the old style when using jena-core only. Keep a mapping of language to class, not classname. Do the external customlanguage class load early (a feature with no known usage).