The class structure of these files is a little strange, and this README
explains it.

Our goal is to make JSON::RPC and XMLRPC::Lite both work with the same code.
(That is, we want to have one WebService API, and have two frontends for it.)

The problem is that these both pass different things for $self to WebService
methods.

When XMLRPC::Lite calls a method, $self is the name of the *class* the
method is in. For example, if we call Bugzilla.version(), the first argument
is Bugzilla::WebService::Bugzilla. So in order to have $self
(our first argument) act correctly in XML-RPC, we make all WebService
classes use base qw(Bugzilla::WebService).

When JSON::RPC calls a method, $self is the JSON-RPC *server object*. In other
words, it's an instance of Bugzilla::WebService::Server::JSONRPC. So we have
Bugzilla::WebService::Server::JSONRPC inherit from Bugzilla::WebService.
