Refactored the Registry::ReadFileCallback, WriteFileCallback and ReaderWriter::Options to they are now defined in their own header and in the osgDB namespace.

Introduced a new FindFileCallback to Registry to compliement the existing ReadFileCallback and WriteFileCallback.

Added support for assign Find, Read and WriteFileCallbacks to osdDB::Options to enable plugins/applications to override the callbacks just for that
read/write call and any nested file operations

src/osgPlugins/ive/PagedLOD.cpp

@@ -16,6 +16,8 @@
 #include "PagedLOD.h"
 #include "Node.h"
 
+#include <osgDB/Options>
+
 using namespace ive;
 
 void PagedLOD::write(DataOutputStream* out)