D5449: pull: fix inconsistent view of bookmarks during pull (issue4700)

[Yuya Nishihara]

>   > IIRC, listkeys is a newer command than lookup. If the peer doesn't support listkeys, I suspect this batch query would fail. In that case, maybe listkeys has to be skipped if the peer doesn't support it and if --bookmark is not specified.
>   
>   listkeys shouldn't need compatibility check in the caller, because it's defined like this in wireprotov1peer.py (https://www.mercurial-scm.org/repo/hg-committed/file/tip/mercurial/wireprotov1peer.py#l381):
>   
>      @batchable
>      def listkeys(self, namespace):
>          if not self.capable('pushkey'):
>              yield {}, None

Yeah, but the batch executor appears not handle such cases.

https://www.mercurial-scm.org/repo/hg-committed/file/tip/mercurial/wireprotov1peer.py#l241