Add ElasticMQ SQS Endpoint

I've been playing with [ElasticMQ](https://github.com/adamw/elasticmq) as a possible SQS replacement in development.

This code is a hack to add an elasticmq endpoint to dream.  To use elasticmq, sqs needs to be configured as follows:

      <sqs-client>
        <privatekey>x</privatekey>  <!-- elasticmq doesn't do auth -->
        <publickey>x</publickey>  <!-- elasticmq doesn't do auth -->
        <accountid>queue</accountid>  <!-- elasticmq assumption -->
        <endpoint>elasticmq</endpoint>  <!-- hardcoded endpoint in dream -->
      </sqs-client>