python-actdiag: bump 0.4.3 -> 0.5.1

Changes:
  0.5.1 (2013-10-22)
  Fix bugs

  0.5.0 (2013-10-05)
  Support python 3.2 and 3.3 (thanks to @masayuko)
  Drop supports for python 2.4 and 2.5
  Replace dependency: PIL -> Pillow

(The test phase still fails for one test, so continue having it disabled.)