Added osgDB::ReaderWriter::Options class to the ReaderWriter base class, support

for settings options in osgDB::Registry, and added the paramter to all of the
reaader/writer plugins.  The Options structure by default has an string attached
for packing basic options, however, it also can be subclassed to encapsulate
any users defined option data. In the later case both the client code *and*
the plugin need to be aware of subclass, the plugin will need to use
dynamic_cast<> to assertain its type.

src/Demos/sgv/sgv.cpp

@@ -298,6 +298,12 @@ int main( int argc, char **argv )
     osg::Timer timer;
     osg::Timer_t before_load = timer.tick();
     
+    // comment out right now, but the following allos users to pass option data to
+    // the ReaderWriter plugins. By default the options are set to NULL. The basic
+    // osgDB::ReaderWriter::Options stucture has just a string, but this can be
+    // subclassed to extend it to handle any options that a user desires.
+    // osgDB::Registry::instance()->setOptions(new osgDB::ReaderWriter::Options("test options"));
+
     osg::Node* rootnode = getNodeFromFiles( argc, argv);
     
     osg::Timer_t after_load = timer.tick();