Log Message:
Update to 0.30

Upstream changes:
0.30  2013-06-24
    - doy/data-visitor should probably be the canonical repository at this
      point

0.29  2013-06-24
    - The class callbacks to be run for an object are now chosen once, at the
      start of visiting that object. Previously, it always looked through the
      entire list of callbacks every time, in a loop in which the object in
      question could be changed by the callback. Since the class callbacks are
      only partially ordered, this lead to differences in whether a callback
      would be called or not based on hash order. reported by Robin Smidsrd.