BDJThreadGroup: error out in waitForShutdown if waiting for current thread to terminate
reduced logging
bdnav: avoid warnings on known but unimplemented extension data
BD-J: fix build against Java 8 rt.jar
BDJ: fix setting File.fs in Java 8 (File.fs is declared final)
BDJ: add FileDescriptor.attach() stub (required by OpenJDK 8)
Implement HToggleGroup
Implement HToggleButton