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/pnm/ReaderWriterPNM.cpp

@@ -6,6 +6,7 @@
 
 #include <osgDB/Registry>
 #include <osgDB/FileNameUtils>
+#include <osgDB/FileUtils>
 
 #include <stdio.h>
 
@@ -24,10 +25,13 @@ class ReaderWriterPNM : public osgDB::ReaderWriter
 				osgDB::equalCaseInsensitive(extension, "pbm"); 
 		}
 
-        virtual ReadResult readImage(const std::string& fileName, const osgDB::ReaderWriter::Options*)
+        virtual ReadResult readImage(const std::string& file, const osgDB::ReaderWriter::Options*)
         {
-            if( !acceptsExtension(osgDB::getFileExtension(fileName) ))
-                return ReadResult::FILE_NOT_HANDLED;
+            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;
 
             FILE *fp = NULL;
 			char line[300];