GUI: better error handling while opening a web browser
workaround for jung library

fixes:
java.util.ConcurrentModificationException
null
java.util.LinkedHashMap$LinkedHashIterator.nextEntry(Unknown Source)
java.util.LinkedHashMap$KeyIterator.next(Unknown Source)
java.util.Collections$UnmodifiableCollection$1.next(Unknown Source)
edu.uci.ics.jung.visualization.control.PickingGraphMousePlugin.mouseDragged(PickingGraphMousePlugin.java:284)
fix popup problems on windows

fixes exceptions like this:

java.awt.IllegalComponentStateException: component must be showing on the
screen to determine its location
component must be showing on the screen to determine its location
java.awt.Component.getLocationOnScreen_NoTreeLock(Component.java:1951)
java.awt.Component.getLocationOnScreen(Component.java:1925)
javax.swing.JPopupMenu.show(JPopupMenu.java:904)
remove superfluous thread
fix typo in error message
ignore all tool tip exceptions for java 1.6.0_27
DRBD: disable add DRBD menu, if DRBD is not available
change debug message level