umbrello/umlwidgets/widgetbase.cpp diagnostics for analyzing bug 429181:

- Static unsigned eventCnt is incremented on each call to
  QGraphicsObjectWrapper::setSelected. It is printed in a debug message
  to ease tracking of the exact call that causes the markers to stick.
- In function QGraphicsObjectWrapper::setSelected print debug message
  containing eventCnt, state, m_calledFromItemChange, and further
  detail.