Finish 1.1.2.
* list properties/classes of strict vocabularies
* A List subject, if specified, must be a node when identifies a valid list within the graph.
A revision to the list update, which allows URI subjects and deals more sanely with initializers.

If a `values` initializer is set with an empty list, `subject` will be used as the first element in the list. Otherwise, if the list is not empty, `subject` identifies the first element of the list to which `values` are prepended yielding a new `subject`. Otherwise, if there are no initial `values`, and `subject` does not identify an existing list in `graph`, `subject` is set to {RDF::NIL}.

This addresses #147.
So that RDF::List.new(foo, graph) can be used to determine if foo is a valid list, do not reset @subject to rdf:nil, but retain the invalid list.

This also affects issue #147.
Version 1.1.2.1.
Finish 1.1.2.1.
A revision to pulled 1.1.2, which allows URI subjects and deals more sanely with initializers.

If a `values` initializer is set with an empty list, `subject` will be used as the first element in the list. Otherwise, if the list is not empty, `subject` identifies the first element of the list to which `values` are prepended yielding a new `subject`. Otherwise, if there are no initial `values`, and `subject` does not identify an existing list in `graph`, `subject` is left as is, but the list will be invalid.