Implement support for NamedMap.isReady()

14.1.1.2206.5 includes an update to the `NamedMap` called `isReady()` returning a boolean.  

If the client is connecting to an older proxy and `isReady()` is called on the client, it should raise an appropriate error stating the operation isn't supported by the current proxy.  Either upgrade the proxy or connect to a proxy that supports this operation.