D3716: ui: add an uninterruptable context manager that can block SIGINT

[durin42 (Augie Fackler)]

durin42 added a comment.


  I'm not in love with uninterruptible as a name (I think unsafeoperation is more explicit) but I don't feel strongly. The rest of the suggestions I liked, so the series is updated and ready for another look.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D3716

To: durin42, #hg-reviewers, indygreg
Cc: spectral, indygreg, yuja, martinvonz, mercurial-devel