Add Fault Code to xmlrpc server for arguments.

Issue Summary

I probably wont be able to patch this as I am unsure of how the fault code/fault generation happens.
Basically just requesting that if the arguments don't match up throw a simple fault code out that say "Argument Failure". At the moment the fault code generated is the default, and it just needs some cleaning up.

Reasoning is quite simple actually when you declare a hook for xmlrpc using core you setup specific types that need to be parsed. When co-workers try this out they usually ignore the types and send everything in as strings the default code is generated. Frustration happens then upon further review the types are matched up and the method works fine.

This would be simple to do as in the post you must specify the types and also in the hook you must. So match the types array with parsed types and that should work right? I say this but again I have no idea how that works so it may be wrong.

Thanks for the help on this and no rush on it.