Deferred copy trouble on Node v0.8

There are [periodic test failures](https://travis-ci.org/tschaub/get-down/jobs/16537742) on Node v0.8 that only occur when testing a rejected `misc.copy` promise.

This looks like an unhandled error in the `oncomplete` method for a socket's write request: 
```
     Uncaught Error: write EBADF
      at errnoException (net.js:770:11)
      at Object.afterWrite (net.js:594:19)
```