Document official support of Neo4j 1.7 and 1.8.
Properly relay undocumented Neo4j error responses.

E.g. a blank 500 response when deleting a relationship.
Aha! Support another undocumented Neo4j error.

Neo4j can throw an exception sometimes (e.g. NullPointerException), and the
error response in those cases don't include a message, but *do* include the
exception name and stack trace; transforming to a friendly error message.