cleared before entering the viewer main loop, this removes memorymanager
a reported memory leak due to the viewer using exit() which bypasses
the clean up on main itself.
Added an osgNew to the ReaderWriterRGB.cpp to aid detected of tracking of
memory leaks.
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.
