D789: merge: add option to abort merge process on failure

[ryanmce (Ryan McElroy)]

ryanmce added a comment.


  Thanks for the feedback @yuja! I'll work on a second version.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D789

To: ryanmce, #hg-reviewers, quark, yuja
Cc: yuja, quark, mercurial-devel