addInterceptor(interceptorFn) {
		if (typeof(interceptorFn) == 'function')
			rpcInterceptorFns.push(interceptorFn);

		return interceptorFn;
	}
Registers a new interceptor function.

@param {LuCI.rpc~interceptorFn} interceptorFn
The interceptor function to register.

@returns {LuCI.rpc~interceptorFn}
Returns the given function value.