Sketch out detaching threads (with partial implementation).

Change-Id: Iafe5f91c8170d4f90155f509ba9e2e3d921af66f
diff --git a/src/jni_internal.cc b/src/jni_internal.cc
index 5ea25e8..8e24e47 100644
--- a/src/jni_internal.cc
+++ b/src/jni_internal.cc
@@ -2183,7 +2183,7 @@
 
   static jint MonitorExit(JNIEnv* env, jobject java_object) {
     ScopedJniThreadState ts(env);
-    Decode<Object*>(ts, java_object)->MonitorEnter();
+    Decode<Object*>(ts, java_object)->MonitorExit();
     return ts.Self()->IsExceptionPending() ? JNI_ERR : JNI_OK;
   }