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
[workspace]
members = ["hg-core", "hg-direct-ffi", "hg-cpython"]
exclude = ["chg", "hgcli"]