Introduced CMake option OSG_PROVIDE_READFILE option that defaults to ON, but when switched to OFF disables the building of the osgDB::read*File() methods,

forcing users to use osgDB::readRef*File() methods.  The later is preferable as it closes a potential threading bug when using paging databases in conjunction
with the osgDB::Registry Object Cache.  This threading bug occurs when one thread gets an object from the Cache via an osgDB::read*File() call where only
a pointer to the object is passed back, so taking a reference to the object is delayed till it gets reassigned to a ref_ptr<>, but at the same time another
thread calls a flush of the Object Cache deleting this object as it's referenceCount is now zero.  Using osgDB::readREf*File() makes sure the a ref_ptr<> is
passed back and the referenceCount never goes to zero.

To ensure the OSG builds when OSG_PROVIDE_READFILE is to OFF the many cases of osgDB::read*File() usage had to be replaced with a ref_ptr<> osgDB::readRef*File()
usage.  The avoid this change causing lots of other client code to be rewritten to handle the use of ref_ptr<> in place of C pointer I introduced a serious of
templte methods in various class to adapt ref_ptr<> to the underly C pointer to be passed to old OSG API's, example of this is found in include/osg/Group:

    bool addChild(Node* child); // old method which can only be used with a Node*

    tempalte<class T> bool addChild(const osg::ref_ptr<T>& child) { return addChild(child.get()); } // adapter template method

These changes together cover 149 modified files, so it's a large submission. This extent of changes are warrent to make use of the Object Cache
and multi-threaded loaded more robust.



git-svn-id: http://svn.openscenegraph.org/osg/OpenSceneGraph/branches/OpenSceneGraph-3.4@15165 16af8721-9629-0410-8352-f15c8da7e697

examples/osgintersection/osgintersection.cpp

@@ -38,7 +38,7 @@ struct MyReadCallback : public osgUtil::IntersectionVisitor::ReadCallback
 {
     virtual osg::Node* readNodeFile(const std::string& filename)
     {
-        return osgDB::readNodeFile(filename);
+        return osgDB::readRefNodeFile(filename).release();
     }
 };
 
@@ -47,37 +47,37 @@ int main(int argc, char **argv)
 {
     // use an ArgumentParser object to manage the program arguments.
     osg::ArgumentParser arguments(&argc,argv);
-    
-    osg::ref_ptr<osg::Node> scene = osgDB::readNodeFiles(arguments);
-    
-    if (!scene) 
+
+    osg::ref_ptr<osg::Node> scene = osgDB::readRefNodeFiles(arguments);
+
+    if (!scene)
     {
         std::cout<<"No model loaded, please specify a valid model on the command line."<<std::endl;
         return 0;
     }
-    
+
     std::cout<<"Intersection "<<std::endl;
-    
-    
+
+
     osg::BoundingSphere bs = scene->getBound();
 
 
     bool useIntersectorGroup = true;
     bool useLineOfSight = true;
-    
+
     //osg::CoordinateSystemNode* csn = dynamic_cast<osg::CoordinateSystemNode*>(scene.get());
     //osg::EllipsoidModel* em = csn ? csn->getEllipsoidModel() : 0;
 
     if (useLineOfSight)
     {
-    
+
         osg::Vec3d start = bs.center() + osg::Vec3d(0.0,bs.radius(),0.0);
         osg::Vec3d end = bs.center() - osg::Vec3d(0.0, bs.radius(),0.0);
         osg::Vec3d deltaRow( 0.0, 0.0, bs.radius()*0.01);
         osg::Vec3d deltaColumn( bs.radius()*0.01, 0.0, 0.0);
 
         osgSim::LineOfSight los;
-        
+
 #if 1
         unsigned int numRows = 20;
         unsigned int numColumns = 20;
@@ -118,7 +118,7 @@ int main(int argc, char **argv)
                 }
             }
         }
-        
+
         {
             // now do a second traversal to test performance of cache.
             osg::Timer_t startTick = osg::Timer::instance()->tick();
@@ -173,7 +173,7 @@ int main(int argc, char **argv)
     else if (useIntersectorGroup)
     {
         osg::Timer_t startTick = osg::Timer::instance()->tick();
-    
+
         osg::Vec3d start = bs.center() + osg::Vec3d(0.0,bs.radius(),0.0);
         osg::Vec3d end = bs.center();// - osg::Vec3d(0.0, bs.radius(),0.0);
         osg::Vec3d deltaRow( 0.0, 0.0, bs.radius()*0.01);
@@ -194,7 +194,7 @@ int main(int argc, char **argv)
             }
         }
 
-        
+
         osgUtil::IntersectionVisitor intersectVisitor( intersectorGroup.get(), new MyReadCallback );
         scene->accept(intersectVisitor);
 
@@ -229,7 +229,7 @@ int main(int argc, char **argv)
                     }
                 }
             }
-        
+
         }
 
     }
@@ -272,6 +272,6 @@ int main(int argc, char **argv)
             }
         }
     }
-    
+
     return 0;
 }