Several fixes.

* [FILE_EXT,FIX] Added file_type(directory) to nested_dir_name/3.
* [OS_EXT,SC] Use swipl native predicate for retrieving the user's home dir.
* [RDF_BUILD,FIX] Regression in rdf_assert_literal/4 would make the predicate recurse.
* [RDF_TMS,FIX] Ordering in rdf_node/5 was wrong (now: first find an RDF triples, and then its TMS node).