Fix ctrl-c tracebacks from downloader processes
Fix ctrl-c tracebacks from downloader processes

- handle broken pipe case

- handle sigint early, so no KeyboardInterrupt
  inside pycurl callbacks that can't be caught.

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