Alter client queue parameters and error reporting

- Use 'queueDisable' as option for disabling client RequestQueue
- Throw more meaningful ConnectionError when enqueue fails

lib/client/client.js

@@ -202,12 +202,11 @@ function Client(options) {
     };
   }
 
-  this.queuing = (options.queuing !== undefined) ? options.queuing : true;
   this.queue = new RequestQueue({
     size: parseInt((options.queueSize || 0), 10),
     timeout: parseInt((options.queueTimeout || 0), 10)
   });
-  if (!this.queuing) {
+  if (options.queueDisable) {
     this.queue.freeze();
   }
 
@@ -1065,7 +1064,7 @@ Client.prototype._send = function _send(message,
   }
   if (!this.socket || !this.connected) {
     if (!this.queue.enqueue(message, expect, emitter, callback)) {
-      callback(new Error('unable to enqueue request'));
+      callback(new ConnectionError('connection unavailable'));
     }
     // Initiate reconnect if needed
     if (this.reconnect) {