timedhosts: sanity check on dl_time
timedhosts: sanity check on dl_time

- handle the dl_time <= 0 case

- relative validity of calculated speed now depends
  on dl_time instead of dl_size.  (that's where the
  random error is)

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