Implement a few of the easy JNI functions.

ExceptionCheck was the next thing we need; the others are just targets of
opportunity.

Change-Id: I1c9e50fd5b5702b6f2afc8b4a31231af2a871b66
diff --git a/src/thread.h b/src/thread.h
index a6e137f..23272f1 100644
--- a/src/thread.h
+++ b/src/thread.h
@@ -135,7 +135,7 @@
   }
 
   bool IsExceptionPending() const {
-    return false;  // TODO exception_ != NULL;
+    return exception_ != NULL;
   }
 
   Object* GetException() const {