D648: blackbox: fix rotation with chg

[quark (Jun Wu)]

quark added a comment.


  I think the original patch was trying to make different `ui` objects use a same file object if their `blackbox.log` path is the same. In theory it could also be problematic in the rotation case. Anyway, that becomes necessary after https://phab.mercurial-scm.org/D650.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D648

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