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

[ryanmce (Ryan McElroy)]

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

INLINE COMMENTS

> ryanmce wrote in test-filemerge-abort.t:22
> Or did you mean this? I guess here I can use `:fail`

Actually I can't because I need an external tool to fail here.

REPOSITORY
  rHG Mercurial

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

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