[PATCH 0 of 8 RFC] introducing VFS for file operations

[FUJIWARA Katsunori]

this patch series is a part of introducing of vfs for WindowsUTF8Plan.

  1. introduce "vfs", and replace direct file API invocations by ones
     via vfs

      1.1 replace "os.XXXX" invocations
      1.2 replace "os.path.XXXX" invocations
      1.3 replace platform depend APIs of "util.XXXX" invocations
      ---- THIS PATCH SERIES IS HERE !!!! ----
      1.4 replace "osutil.XXXX" invocations
      1.5 replace builtin "file()"/"open()" invocations
      1.6 replace "shutil.XXXX" invocations
          copy(), copyfile(), copystat(), copymode(), rmtree() are used
      1.7 replace "tempfile.XXXX" invocations
          filenames in working directory are used as prefix by:
          - filemerge.filemerge()
          - scmutil.opener.__call__(): via util.mktempcopy()

  2. extend opener to be used for all repository related file operations
  3. introduce unicode subclass of vfs
  4. implement vfs switching by UTF-8 safe-ness of dirstate

# http://mercurial.selenic.com/wiki/WindowsUTF8Plan
# http://www.selenic.com/pipermail/mercurial-devel/2011-December/036385.html

I want to confirm whether these patches are ones supposed in
WindowsUTF8Plan, and I can continue along this line, or not.

in addition to them, some questions are also described in each patch
descriptions.

this patch series can be applied on 622aa57a90b1.

# tested only on Linux environment