copy: add experimetal support for unmarking committed copies The simplest way I'm aware of to unmark a file as copied after committing is this: hg uncommit --keep <dest> hg forget <dest> hg add <dest> hg amend This patch teaches `hg copy --forget` a `-r` argument to simplify that into: hg copy --forget --at-rev . <dest> In addition to being simpler, it doesn't touch the working copy, so it can easily be used even if the destination file has been modified in the working copy. I'll teach `hg copy` without `--forget` to work with `--at-rev` next. Differential Revision: https://phab.mercurial-scm.org/D8030

--- a/tests/test-completion.t	Fri Dec 20 15:50:13 2019 -0800
+++ b/tests/test-completion.t	Tue Jan 28 14:07:57 2020 -0800
@@ -257,7 +257,7 @@
   commit: addremove, close-branch, amend, secret, edit, force-close-branch, interactive, include, exclude, message, logfile, date, user, subrepos
   config: untrusted, edit, local, global, template
   continue: dry-run
-  copy: forget, after, force, include, exclude, dry-run
+  copy: forget, after, at-rev, force, include, exclude, dry-run
   debugancestor: 
   debugapplystreamclonebundle: 
   debugbuilddag: mergeable-file, overwritten-file, new-file