Make CheckJNI and JNI workarounds mutually exclusive...

...in the opposite direction; needing workarounds turns off CheckJNI.
This isn't necessarily a good idea, but I like the cleanup parts of
this change.

Change-Id: I708235ea3e5cc35ef90b01dd810e097e3ff9dd26
diff --git a/src/monitor.cc b/src/monitor.cc
index 7261bc4..6a7b66f 100644
--- a/src/monitor.cc
+++ b/src/monitor.cc
@@ -28,6 +28,7 @@
 #include "mutex.h"
 #include "object.h"
 #include "object_utils.h"
+#include "scoped_thread_list_lock.h"
 #include "stl_util.h"
 #include "thread.h"
 #include "thread_list.h"