bookmarks: allow pushkey if new equals current Previously a bookmark pushkey would be rejected if the specified 'old' value didn't match the servers 'current' value. This change allows this situation, as long as the 'current' server value equals the 'new' pushkey value already. We are trying to write a hook that forces a server bookmark to move forward, using a changegroup hook. If the user also pushed the bookmark, they would get an error, since they computed their pushkey (old,new) pair before the server moved the bookmark. Long term, bundle2 will let us do this more smartly, but this change seems reasonable for now.