nodemap: track the tip_node for validation
Differential Revision: https://phab.mercurial-scm.org/D8184
https://bz.mercurial-scm.org/1089 $ hg init $ mkdir a $ echo a > a/b $ hg ci -Am m adding a/b $ hg rm a removing a/b $ hg ci -m m a $ mkdir a b $ echo a > a/b $ hg ci -Am m adding a/b $ hg rm a removing a/b $ cd bRelative delete: $ hg ci -m m ../a $ cd ..