Better macro support for switching on/off use of mutex

include/osg/Referenced

@@ -14,12 +14,15 @@
 #ifndef OSG_REFERENCED
 #define OSG_REFERENCED 1
 
-#include <OpenThreads/ScopedLock>
-#include <OpenThreads/Mutex>
 
 #include <osg/Export>
 
-// #define USE_REF_MUTEX 1
+// #define THREAD_SAFE_REF_UNREF 1
+
+#ifdef THREAD_SAFE_REF_UNREF
+    #include <OpenThreads/ScopedLock>
+    #include <OpenThreads/Mutex>
+#endif
 
 namespace osg {
 
@@ -58,7 +61,7 @@ class SG_EXPORT Referenced
             this object has another pointer which is referencing it.*/
         inline void ref() const
         { 
-#ifdef USE_REF_MUTEX
+#ifdef THREAD_SAFE_REF_UNREF
             OpenThreads::ScopedLock<OpenThreads::Mutex> lock(_refMutex); 
 #endif
             ++_refCount;
@@ -85,7 +88,7 @@ class SG_EXPORT Referenced
     protected:
         virtual ~Referenced();
         
-#ifdef USE_REF_MUTEX
+#ifdef THREAD_SAFE_REF_UNREF
         mutable OpenThreads::Mutex  _refMutex;
 #endif
         mutable int                 _refCount;
@@ -122,7 +125,7 @@ inline void Referenced::unref() const
 {
     bool needDelete = false;
     {
-#ifdef USE_REF_MUTEX
+#ifdef THREAD_SAFE_REF_UNREF
         OpenThreads::ScopedLock<OpenThreads::Mutex> lock(_refMutex); 
 #endif
         --_refCount;