py3: open chistedit file in binary mode using vfs

We write bytes to the file, so it should be open in binary
mode. Opening it via the vfs takes care of that for us.

Now you'll get yet a different traceback if you try to confirm you
histedit plan.

Differential Revision: https://phab.mercurial-scm.org/D7185

hgext/histedit.py

@@ -1684,11 +1684,10 b' def _chistedit(ui, repo, *freeargs, **op'
         if type(rc) is list:
             ui.status(_(b"performing changes\n"))
             rules = makecommands(rc)
-            filename = repo.vfs.join(b'chistedit')
-            with open(filename, b'w+') as fp:
+            with repo.vfs(b'chistedit', b'w+') as fp:
                 for r in rules:
                     fp.write(r)
-            opts[b'commands'] = filename
+                opts[b'commands'] = fp.name
             return _texthistedit(ui, repo, *freeargs, **opts)
     except KeyboardInterrupt:
         pass