D4125: narrow: add '--extend' flag to tracked command

[pulkit (Pulkit Goyal)]

pulkit added a comment.


  In https://phab.mercurial-scm.org/D4125#64732, @durin42 wrote:
  
  > Seems fine to me, though thinking we should probably spend some time to make sure the sparse and narrow patterns are cross-compatible like this change seems to hope for.
  
  
  I already did that. https://www.mercurial-scm.org/repo/hg-committed/rev/f64ebe7d2259

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D4125

To: pulkit, durin42, #hg-reviewers
Cc: martinvonz, mercurial-devel