8043224: -Xcheck:jni improvements to exception checking and excessive local refs

Warning when not checking exceptions from function that require so, also when local refs expand beyond capacity.

Reviewed-by: zgu, coleenp, hseigel

hotspot/src/share/vm/runtime/thread.cpp

@@ -1448,6 +1448,7 @@ void JavaThread::initialize() {
   _thread_stat = new ThreadStatistics();
   _blocked_on_compilation = false;
   _jni_active_critical = 0;
+  _pending_jni_exception_check_fn = NULL;
   _do_not_unlock_if_synchronized = false;
   _cached_monitor_info = NULL;
   _parker = Parker::Allocate(this) ;