headssummary: directly feed the function with the 'pushop' object Our goal is to be able to perform the post processing directly into the '_headssummary' function. However before this patch the '_headsummary' function only had access to repo, remote, outgoing while the '_postprocessobsolete' function takes a 'pushop' object. Experience shows that having the 'pushop' object helps extensions so we update '_headssummary' to take a pushop object as argument.