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

include/osg/Object

@@ -92,8 +92,8 @@ class OSG_EXPORT Object : public Referenced
 
         /** return the compound class name that combines the library name and class name.*/
         std::string getCompoundClassName() const { return std::string(libraryName()) + std::string("::") + std::string(className()); }
-        
-        
+
+
         /** Convert 'this' into a Node pointer if Object is a Node, otherwise return 0.
           * Equivalent to dynamic_cast<Node*>(this).*/
         virtual Node* asNode() { return 0; }
@@ -168,6 +168,8 @@ class OSG_EXPORT Object : public Referenced
         /** set the UserDataContainer object.*/
         void setUserDataContainer(osg::UserDataContainer* udc);
 
+        template<class T> void setUserDataContainer(const ref_ptr<T>& udc) { setUserDataContainer(udc.get()); }
+
         /** get the UserDataContainer attached to this object.*/
         osg::UserDataContainer* getUserDataContainer() { return _userDataContainer; }
 
@@ -187,6 +189,8 @@ class OSG_EXPORT Object : public Referenced
          */
         virtual void setUserData(Referenced* obj);
 
+        template<class T> void setUserData(const ref_ptr<T>& ud) { setUserData(ud.get()); }
+
         /** Get user data.*/
         virtual Referenced* getUserData();