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.
$ rm -rf a
$ hg init a
$ cd a
$ echo a > a
$ hg ci -Am0
adding a
$ hg tag t1 # 1
$ hg tag --remove t1 # 2
$ hg co 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg tag -f -r0 t1
$ hg tags
tip 3:a49829c4fc11
t1 0:f7b1eb17ad24
$ cd ..