D816: histedit: add copy histedit action

[mbthomas (Mark Thomas)]

mbthomas added inline comments.

INLINE COMMENTS

> durin42 wrote in histedit.py:864
> Shouldnt't we only allow copying things from outside the histedit stack?

I allowed copy to refer to things in the stack because it's conceivable you might want something from the stack twice.  Thinking about it now, this is only actually useful if the `base` action is enabled (`experimental.histeditng=true`), in which case you could write something like:

  pick 222
  pick 111
  base aaa
  copy 222
  copy 111

I could add a check that only fires if `histeditng` is disabled.  Does that sound useful?

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D816

To: mbthomas, #hg-reviewers, ryanmce
Cc: durin42, ryanmce, mercurial-devel