Fix/improve exception detail messages for unboxing.

This fixes libcore/luni/src/test/java/libcore/java/lang/reflect/MethodTest.java
failures.

Change-Id: Idf6aae169bd72f0534d4094170536e6b2515ca07
diff --git a/src/reflection.h b/src/reflection.h
index e832c3d..a286a57 100644
--- a/src/reflection.h
+++ b/src/reflection.h
@@ -28,7 +28,7 @@
 
 void InitBoxingMethods();
 void BoxPrimitive(JNIEnv* env, Primitive::Type src_class, JValue& value);
-bool UnboxPrimitive(JNIEnv* env, Object* o, Class* dst_class, JValue& unboxed_value);
+bool UnboxPrimitive(JNIEnv* env, Object* o, Class* dst_class, JValue& unboxed_value, const char* what);
 
 bool ConvertPrimitiveValue(Primitive::Type src_class, Primitive::Type dst_class, const JValue& src, JValue& dst);