title: How do I compare two git repositories?
body: <p>I've got two different exports of our CVS repository into git.  They diverge at some point, and I'm doing some investigation into why.  The development line goes back several years and over tens of thousands of commits.</p>
  
  <p>At the beginning of the development line, the SHA1 IDs for each commit are identical, telling me that git-cvsimport is very consistent about what it is doing when it reads the results of cvsps and imports.</p>
  
  <p>But sometime between the first commit and yesterday, the SHA1 IDs begin to diverge.  I'd like to find out where this is by comparing a list of commit IDs from each repository and looking to see what's missing.  Are there any good tools or techniques for doing this?</p>