JNI Specification for DetachCurrentThread needs modification in relation to pending exceptions

Currently the JNI specification indicates that, unless listed otherwise, no JNI method should be called with a pending exception. DetachCurrentThread is not listed as allowing a pending exception, but the implementation of DetachCurrentThread in hotspot implements the "uncaught exception handling" that is expected in Java threads - via Thread->exit() call which invokes JavaThread::exit

The uncaught exception handling is highly desirable so we do not want to change the behaviour of the VM.

But it is probably too strong to mandate that DetachCurrentThread must do uncaught exception handling.

So at a minimum we need to add DetachCurrentThread to the set of methods that can be called safely with a pending exception.