Fix for adding event listeners on every reconnect.

The current reconnect logic adds listeners for the ```possibleAuthErrorHandler``` on every reconnect. This eventually makes event emitter scream about listener leak.

The problem shows like this after about 11 reconnects.

```
warning: possible EventEmitter memory leak detected. 11 listeners added. Use emitter.setMaxListeners() to increase limit.
Trace
    at Connection.EventEmitter.addListener (events.js:160:15)
    at Connection.connect (/Users/martin/dev/scanpix/locko/node_modules/amqp/amqp.js:1070:10)
    at Connection.reconnect (/Users/martin/dev/scanpix/locko/node_modules/amqp/amqp.js:1038:8)
    at null._onTimeout (/Users/martin/dev/scanpix/locko/node_modules/amqp/amqp.js:876:16)
    at Timer.listOnTimeout [as ontimeout] (timers.js:110:15)
```