narrow: use repo.local() instead of isinstance()

narrow: use repo.local() instead of isinstance()

Differential Revision: https://phab.mercurial-scm.org/D2973

--- a/hgext/narrow/__init__.py	Fri Mar 30 11:33:21 2018 -0700
+++ b/hgext/narrow/__init__.py	Fri Mar 30 11:15:58 2018 -0700
@@ -71,7 +71,7 @@
 
 def reposetup(ui, repo):
     """Wraps local repositories with narrow repo support."""
-    if not isinstance(repo, localrepo.localrepository):
+    if not repo.local():
         return
 
     narrowrepo.wraprepo(repo)