D5516: fix: add some arguments to facilitate extensions

[durin42 (Augie Fackler)]

durin42 added a comment.


  I'm -0 on this: what's special about this functionality that it needs to be an extension of an extension instead of something that can be done in core?

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D5516

To: hooper, #hg-reviewers
Cc: durin42, mercurial-devel