merge: introduce a clean_update() for that use-case I find it hard to understand what value to pass for all the arguments to `merge.update()`. I would like to introduce functions that are more specific to each use-case. We already have `graft()`. This patch introduces a `clean_update()` and uses it in some places to show that it works. Differential Revision: https://phab.mercurial-scm.org/D7902