Small "git clean" annoyance

[Linus Torvalds <torvalds@linux-foundation.org>]

I don't have a patch for this, and I guess it doesn't much matter, but
I just found this annoying:

  [torvalds@i5 git]$ mkdir -m 0 tmp
  [torvalds@i5 git]$ git clean -dqfx
  warning: failed to remove tmp/
  [torvalds@i5 git]$ rmdir tmp

and the reason is simply that git gives up if the directory is
unreadable and thus cannot be opened.

Which is kind of understandable, but at the same time, if it's empty,
a "rmdir()" will just work. So git gave up a bit too soon.

(In case anybody wonders, the reason I had empty unreadable
directories around is not because I commonly do "mkdir -m 0", but
simply because they got created when I was running a system call
fuzzer for testing).

Now, I realize that if the directory isn't empty, and is unreadable,
we really should give up (although a better error message about _why_
we failed may be in order) rather than try to chmod it or anything
like that. But the simple "try to rmdir it" might be a good addition
for the trivial case.

                     Linus