narrow: keep narrowspec backup in store

As suggested by Yuya in review of D4099.

Differential Revision: https://phab.mercurial-scm.org/D5470

mercurial/narrowspec.py

@@ -160,19 +160,19 b' def save(repo, includepats, excludepats)'
 def savebackup(repo, backupname):
     if repository.NARROW_REQUIREMENT not in repo.requirements:
         return
-    vfs = repo.vfs
-    vfs.tryunlink(backupname)
-    util.copyfile(repo.svfs.join(FILENAME), vfs.join(backupname), hardlink=True)
+    svfs = repo.svfs
+    svfs.tryunlink(backupname)
+    util.copyfile(svfs.join(FILENAME), svfs.join(backupname), hardlink=True)
 
 def restorebackup(repo, backupname):
     if repository.NARROW_REQUIREMENT not in repo.requirements:
         return
-    util.rename(repo.vfs.join(backupname), repo.svfs.join(FILENAME))
+    util.rename(repo.svfs.join(backupname), repo.svfs.join(FILENAME))
 
 def clearbackup(repo, backupname):
     if repository.NARROW_REQUIREMENT not in repo.requirements:
         return
-    repo.vfs.unlink(backupname)
+    repo.svfs.unlink(backupname)
 
 def restrictpatterns(req_includes, req_excludes, repo_includes, repo_excludes):
     r""" Restricts the patterns according to repo settings,

tests/test-narrow-clone-stream.t

@@ -77,6 +77,7 b' Making sure store has the required files'
   00manifest.i
   data (tree flat-fncache !)
   fncache (tree flat-fncache !)
+  journal.narrowspec
   meta (tree !)
   narrowspec
   undo