t4006: resurrect commented-out tests

t4006: resurrect commented-out tests

This set of tests was added by 4434e6ba6c (tests: check --[short]stat
output after chmod, 2012-05-01), and is primarily about the handling of
binary versus text files.

Later, 74faaa16f0 (Fix "git diff --stat" for interesting - but empty -
file changes, 2012-10-17) changed the stat output so that the empty text
file is mentioned rather than omitted. That commit just comments out
these tests. There's no discussion in the commit message, but the
original email[1] says:

  NOTE! This does break two of our tests, so we clearly did this on
  purpose, or at least tested for it. I just uncommented the subtests
  that this makes irrelevant, and changed the output of another one.

I don't think they're irrelevant, though. We should be testing this
"mode change only" case and making sure that it has the post-74faaa16f0
behavior. So this commit brings back those tests, with the current
expected output.

[1] https://public-inbox.org/git/CA+55aFz88GPJcfMSqiyY+u0Cdm48bEyrsTGxHVJbGsYsDg=Q5w@mail.gmail.com/

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>