subrepo: use vfs.walk instead of os.walk

"dirpath" in the tuple yielded by "vfs.walk()" is relative one from
the root of specified vfs, and absolute path in the warning message is
composed by "vfs.join()".

On the other hand, target file "f" exists in "dirpath", and
"reljoin()" is needed to unlink "f" by "vfs.unlink()".

mercurial/subrepo.py

@@ -303,7 +303,7 b' def _abssource(repo, push=False, abort=T'
         raise util.Abort(_("default path for subrepository not found"))
 
 def _sanitize(ui, vfs, ignore):
-    for dirname, dirs, names in os.walk(vfs.base):
+    for dirname, dirs, names in vfs.walk():
         for i, d in enumerate(dirs):
             if d.lower() == ignore:
                 del dirs[i]
@@ -313,8 +313,8 b' def _sanitize(ui, vfs, ignore):'
         for f in names:
             if f.lower() == 'hgrc':
                 ui.warn(_("warning: removing potentially hostile 'hgrc' "
-                          "in '%s'\n") % dirname)
-                os.unlink(os.path.join(dirname, f))
+                          "in '%s'\n") % vfs.join(dirname))
+                vfs.unlink(vfs.reljoin(dirname, f))
 
 def subrepo(ctx, path):
     """return instance of the right subrepo class for subrepo in path"""