Martin von Zweigbergk <martinvonz@google.com> [Sun, 17 Jun 2018 21:47:34 -0700] rev 38376
debugbuilddag: use context manager for progress, locks, transaction
I minor side-effect is that .hg/localtags is now written before the
transaction commits.
Differential Revision: https://phab.mercurial-scm.org/D3777