Enforce the use of accessors on JValue so we can ensure sign extension.

Change-Id: I34810af7661d8674c84707afe5cfdf9e2c233f8b
diff --git a/src/thread.cc b/src/thread.cc
index a4194b1..1a39d99 100644
--- a/src/thread.cc
+++ b/src/thread.cc
@@ -878,8 +878,8 @@
   // Call the handler.
   Method* m = handler->GetClass()->FindVirtualMethodForVirtualOrInterface(gUncaughtExceptionHandler_uncaughtException);
   JValue args[2];
-  args[0].l = peer_;
-  args[1].l = exception;
+  args[0].SetL(peer_);
+  args[1].SetL(exception);
   m->Invoke(this, handler, args, NULL);
 
   // If the handler threw, clear that exception too.
@@ -897,7 +897,7 @@
   if (group != NULL) {
     Method* m = group->GetClass()->FindVirtualMethodForVirtualOrInterface(gThreadGroup_removeThread);
     JValue args[1];
-    args[0].l = peer_;
+    args[0].SetL(peer_);
     m->Invoke(this, group, args, NULL);
   }
 }