Here's a nice fresh minor update.

Notes on this third patch:

* The docstrings are now done.

* I discovered that fchmodat() doesn't actually support
  AT_SYMLINK_NOFOLLOW!  glibc documents using the flag, then
  comically notes that it doesn't actually work.  Specifying
  it results in ENOTSUP every time.  os.chmod() now accomodates
  this; it throws NotImplementedError if it detects this situation.
  However it should also Just Work once glibc supports it.

* While editing the docstrings, I noticed that several of them
  had old-style octal constants ;-)  I fixed 'em.

* I added support for the remove_dir argument to unlink/remove
  on Windows.  I also made it work on non-Windows even when
  unlinkat() is not available.