dummyserver.js: /endAfterHeaders: really don't send any response entity
dummyserver.js: /endAfterHeaders: really don't send any response entity

fixes this spec on Firefox 34:
"err" argument in "finished" callback
 - is set to Error("network error") when connection ends after sending headers (same-origin)

jakutis/httpinvoke,fuzeman/httpinvoke,fuzeman/httpinvoke,jakutis/httpinvoke