stop urlgrabber from leaking file objections when an error occurs during do_perform from rh bug https://bugzilla.redhat.com/show_bug.cgi?id=617844
stop urlgrabber from leaking file objections when an error occurs during do_perform
from rh bug https://bugzilla.redhat.com/show_bug.cgi?id=617844

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