Make it easier to debug jni.

The ExceptionDescribe call dumps the java stacktrace, which is
really useful when you're trying to figure out what exactly
failed.

Also, jValue used to return a bool, swallowing errors for no
apparent reason.  I've changed that to return an error.

MultiPart: 1/2
Change-Id: I9c4451fd739bf6108b753ba13fc73adaafdc1423
5 files changed