Recent commit causes smach_viewer to crash

[pirobot]

Hello,

A recent commit (7ce3355) causes smach_viewer.py to crash with the following:

Traceback (most recent call last):
  File "/opt/ros/indigo/lib/smach_viewer/smach_viewer.py", line 974, in <module>
    main()
  File "/opt/ros/indigo/lib/smach_viewer/smach_viewer.py", line 964, in main
    frame = SmachViewerFrame()
  File "/opt/ros/indigo/lib/smach_viewer/smach_viewer.py", line 522, in __init__
    self.widget = xdot.wxxdot.WxDotWindow(graph_view, -1)
AttributeError: 'module' object has no attribute 'wxxdot'

[k-okada]

please consider merging #11

[k-okada]

@furushchev