Fix bug with ASF's per-traverse object: t+

Bug reported in marpa-parser group email from Ruslan Shvedov
  Date: Thu, 16 Jan 2014 17:06:41 +0200
  Message-ID: <CALTky2dEjkxTYmrx=EKxLrGaV39HtoK2i=4YvXrLr5i4T9_F=g@mail.gmail.com>