g.tx() doesn't start remote transactions

Neither g.tx() nor tx().begin() technically start a transaction on the server. they only do some basic setup for the the remote GraphTraversalSource. the lazy way in which connections are created by the connection pool are still at play. the connection and session do not technically get created until Gremlin is actually sent which is unintuitive. Seems like folks would more likely expect begin() to trigger the start of the transaction on the server.