Introspection Patch for XML-RPC, current to SVN 2005-12-29 (r359943)

I've taken Aaron Hamid's Introspection patch (which was in turn derived from the one here: http://xmlrpc-c.sourceforge.net/hacks/helma-xmlrpc-introspection.diff ) and basically rewritten it to work with the current XML-RPC library.

I tried to set it up so that it followed the existing coding style as much as possible, and would not break any existing applications. For example, when I needed a list of handlers supported by a particular mapping, I added a new interface XmlRpcListableHandlerMapping that provides this information, made the default handler implement it, and designed my code so that if it were not implemented by a handler in use, everything would work except the system.listMethods functionality that relies on it.

I hope you will be able to integrate this code into the next version of the library; please contact me with any questions or issues. I will be attaching the patch to this issue if I can so that the problem with his previous patch will not occur.