debugindex: add --format flag to allow debugging parentdelta
-f 1 shows extra data from revlogv1 (aka revlogng) including flags and size
(based on a patch by Pradeepkumar Gayam <in3xes@gmail.com>)
$ 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 -r0 t1
$ hg tags
tip 3:a49829c4fc11
t1 0:f7b1eb17ad24