Fixed crash the occurred when passing in a osgDB::Options to the ObjectCache that doesn't have any references to it.

include/osgDB/ObjectCache

@@ -70,14 +70,17 @@ class OSGDB_EXPORT ObjectCache : public osg::Referenced
 
         typedef std::pair<std::string, osg::ref_ptr<const osgDB::Options> >   FileNameOptionsPair;
 
-        class ClassComp {
-        public:
+        struct ClassComp
+        {
             bool operator() (const ObjectCache::FileNameOptionsPair& lhs, const ObjectCache::FileNameOptionsPair& rhs) const;
         };
 
+
         typedef std::pair<osg::ref_ptr<osg::Object>, double >           ObjectTimeStampPair;
         typedef std::map<FileNameOptionsPair, ObjectTimeStampPair, ClassComp>     ObjectCacheMap;
 
+        ObjectCacheMap::iterator find(const std::string& fileName, const osgDB::Options* options);
+
         ObjectCacheMap                          _objectCache;
         OpenThreads::Mutex                      _objectCacheMutex;