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/osg/Shader.cpp

@@ -121,7 +121,9 @@ Shader::~Shader()
 
 bool Shader::setType( Type t )
 {
-    if( _type != UNDEFINED )
+    if (_type==t) return true;
+
+    if (_type != UNDEFINED)
     {
         osg::notify(osg::WARN) << "cannot change type of Shader" << std::endl;
         return false;