System.exit(0) alternative

[maartentbm]

FindBugs does not like a call to System.exit. However, if we just dispose the Window, there is a memory leak, which is solved by System.exit because it kills the JVM. An alternative way of calling System.exit which is not "wrong" or an alternative for it in general would be nice. #FindBugsPleasing

"This should only been done when it is appropriate." - Findbugs (http://findbugs.sourceforge.net/bugDescriptions.html#DM_EXIT)