Handle case where server responds while the request is still being sent (usually SERVER_ERROR)
  Forward response, cancel send, and cleanup connection
Refixed in a simpler way by just closing the server connection on any stray response
Changes as suggested by review:
 set err for connection to EINVAL
 cleanups
Merge pull request #150 from jdi-tagged/early-response

Handle case where server responds while the request is still being sent. You encounter this scenario with memcache when you send it an item that exceeds maximum slab size item