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

[pulkit (Pulkit Goyal)]

pulkit added inline comments.

INLINE COMMENTS

> foozy wrote in narrowcommands.py:303
> Just curious, is it intentional that the name of this option is different from `--import-rules` of debugsparse ?

I didn't know about that. That likes a good name, @martinvonz what do you think?

REPOSITORY
  rHG Mercurial

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

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