bookmarks: introduce listbinbookmarks()
`bookmarks` bundle2 part will work with binary nodes. To avoid unnecessary
conversions between binary and hex nodes let's add `listbinbookmarks()` that
returns binary nodes. For now this function is a copy-paste of
listbookmarks(). In the next patch this copy-paste will be removed.
ERROR: FIXME: This is a known failure of filelog.size for data starting with \1\n
OK.