title: git gc error: failed to run repack message
body: <p>I've just run <code>git gc</code> on my local repository to do some regular clean-up. Today for the first time, it failed. Here's what I've done: (Windows 7)</p>
  
  <pre><code>C:\Source\TxTranslation&gt;git gc
  Counting objects: 880, done.
  Delta compression using up to 8 threads.
  Compressing objects: 100% (540/540), done.
  Writing objects: 100% (880/880), done.
  Total 880 (delta 504), reused 589 (delta 333)
  rm: cannot unlink `pack-18179305b5b5dbdaf059e4ded50b736ab93e220c.pack': Permission denied
  
  C:\Source\TxTranslation&gt;git gc
  Counting objects: 880, done.
  Delta compression using up to 8 threads.
  Compressing objects: 100% (369/369), done.
  Writing objects: 100% (880/880), done.
  Total 880 (delta 504), reused 880 (delta 504)
  mv: cannot move `/c/Source/TxTranslation/.git/objects/pack/pack-3002d22690e007a4205f6ecfa19d6e93296fdd78.pack' to `/c/Source/TxTranslation/.git/objects/pack/old-pack-3002d22690e007a4205f6ecfa19d6e93296fdd78.pack'
  error: failed to run repack
  </code></pre>
  
  <p>I can retry it as often as I want, I always get the second output again. The "permission denied" error above is nonsense. I believe it's a common spurious error that I see on many Windows systems these days. It may be coming from virus scanners that keep files open so that they can't be deleted immediately. That leads to all sorts of issues but apparently can't be avoided.</p>
  
  <p>Is this a problem? Is something broken? I absolutely don't understand what those message mean to me. Browsing the log with diffs still works. What could I do to fix that problem? (Luckily I have pushed everything to Github just before, so I could simply re-clone it, but I'd like to try fixing it first, in case it happens again.)</p>