D2701: merge: use constants for actions

[indygreg (Gregory Szorc)]

indygreg marked an inline comment as done.
indygreg added inline comments.

INLINE COMMENTS

> phillco wrote in merge.py:909
> Update this too?

Done.

What's... amusing is that ``dr`` and ``rd`` are not actions in the current code base.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D2701

To: indygreg, #hg-reviewers, phillco
Cc: phillco, pulkit, mercurial-devel