serf_get: Fix counting of completed requests.
serf_get: Fix counting of completed requests.

* test/serf_get.c
  (handler_baton_t): Rename requests_outstanding to completed_requests.
  (handle_response): Increment completed_requests when request fully read.
  (setup_request): Remove requests_outstanding usage.
  (main): Exit when completed_requests equals to number of submitted 
   requests.

jandre/serf,jandre/serf,jandre/serf,jandre/serf