Get rid of "HTTP 200 OK" errors.  BZ 871835.
Get rid of "HTTP 200 OK" errors.  BZ 871835.

When the server drops connection after sending "HTTP 200 OK",
pycurl raises error 18 with empty error message.  Urlgrabber
assumes it's a HTTP error.

Add an explicit check for 2xx codes, and report the underlying
error instead (Partial file).

tradej/urlgrabber,Distrotech/urlgrabber,oe-lite/urlgrabber,tradej/urlgrabber,Distrotech/urlgrabber,oe-lite/urlgrabber,oe-lite/urlgrabber,Distrotech/urlgrabber,oe-lite/urlgrabber,Distrotech/urlgrabber,tradej/urlgrabber,henrysher/urlgrabber,henrysher/urlgrabber,henrysher/urlgrabber,henrysher/urlgrabber