tested the last bit, works fine in stable and main

Does merge of files added to a renamed directory work now?
(I guess yes, but didn't verify)

merge following renamed files is in main now and enabled by default.
TODO: merge of files added to a renamed directory.

Proposal for two kinds of behaviour for diff command.  1: follow renames. 2:
honour only path names.

Proposal for applying changes to renamed/copied files: try to apply every hunk
to every renamed/copied destination.  Don't know if this should happen over the
transitive closure of copies, but probably; if not, multiple renames won't
obviously work, though.

If you rename a file locally and remote changes it, update should modify the
renamed file. And vice versa.