[PATCH 0 of 6 V2] localrepo: a part of migration to "vfs" for WindowsUTF8Plan

[FUJIWARA Katsunori]

This patch series is a part of migration from "opener" to "vfs" for
WindowsUTF8Plan. this focuses around the constructor of
localrepository class.

This posting is different from past one in points below:

  - separate re-fixing issue2528 from migration itself
  - separate replacing "opener" referring from adding new API to vfs
  - add replacing "os.path.join()" by "self.wvfs.join()"

Changing around "ui.readconfig()" invoked from the constructor of
localrepository is also avoided in this series, because it is also
called from other than localrepository constructor and it is not clear
how default vfs object should be created for such invocations at the
present time.

I'll change it when users of it are migrated enough.