Add Support for Thrift

This adds support for the Thrift protocol. To use Thrift, set your host to `thrift://`, and set the 'connectionClass' to 'thrift', like this:

```
var client = new elasticsearch.Client({
  'host': 'thrift://localhost:9200',
  'connectionClass': 'thrift',
  'onThriftError': function(err) { logger.warn('Thrift error.', err) },
  'onThriftConnect': function() { logger.info('Thrift connection is online.'); }
});
```