Changed tornado/simple_httpclient.py to raise the error instead of
storing the error message and then raising an HTTPError. 
Changed the websocket tests for network_fail and network timeout to
expect an IOError instead of an HTTPError.
Merge pull request #1042 from moijes12/fix1033_2

Changed _on_close method tornado/simple_httpclient.py to raise the error instead of raising an HTTPError