Add log-on-failure versions of RDF node and statement creation functions.
Express class derivation in Turtle.
Add safe destruction wrappers for freeing librdf primitives.
Use libtwine wrappers for creating/destroying nodes and statements.
Handle zero-priority (i.e., immediate-add) resource references.
Handle resource references which require proxies.
Add foaf:topic handling; use SELECT DISTINCT when querying for existing data.