[CURATOR-160] Add builders and dsl for ZooKeeper's config and reconfig m...

...ethods.
It's optional. Here's the Javadoc comment:

```
     * @param fromConfig
     *                version of the current configuration (optional - causes reconfiguration to throw an exception if configuration is no longer current)
```

Also, in the ZK code, 

```
                long configId = reconfigRequest.getCurConfigId();
  
                if (configId != -1 && configId!=lzks.self.getLastSeenQuorumVerifier().getVersion()){
```