Moved the responsibility for finding file to load on to the ReaderWriter plugins,

instead of osgDB::Registry where it original lay.  This has been done to allow
fileName strings to be encode data rather than just file names, such as one
requires when using PagedLOD along with plugins for doing dynamic tesselation.

src/osgPlugins/dds/ReaderWriterDDS.cpp

@@ -20,6 +20,7 @@
 
 #include <osgDB/Registry>
 #include <osgDB/FileNameUtils>
+#include <osgDB/FileUtils>
 
 #include <stdio.h>
 
@@ -324,8 +325,14 @@ class ReaderWriterDDS : public osgDB::ReaderWriter
             return osgDB::equalCaseInsensitive(extension,"dds"); 
         }
 
-        virtual ReadResult readImage(const std::string& fileName, const osgDB::ReaderWriter::Options*)
+        virtual ReadResult readImage(const std::string& file, const osgDB::ReaderWriter::Options*)
         {
+            std::string ext = osgDB::getLowerCaseFileExtension(file);
+            if (!acceptsExtension(ext)) return ReadResult::FILE_NOT_HANDLED;
+
+            std::string fileName = osgDB::findDataFile( file );
+            if (fileName.empty()) return ReadResult::FILE_NOT_FOUND;
+
             osg::Image* osgImage = ReadDDSFile(fileName.c_str());
             if (osgImage==NULL) return ReadResult::FILE_NOT_HANDLED;
             return osgImage;