D1224: merge: cache unknown dir checks (issue5716)

[durin42 (Augie Fackler)]

durin42 requested changes to this revision.
durin42 added a comment.
This revision now requires changes to proceed.


  needs rebased, otherwise looks fine

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D1224

To: mbthomas, #hg-reviewers, durin42
Cc: durin42, sid0, krbullock, mercurial-devel