D3586: patch: use slicing to check patch line prefixes

[yuja (Yuya Nishihara)]

yuja added a comment.


  This appears to conflict with https://phab.mercurial-scm.org/D3580.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D3586

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