title: Which code is shared between the original Git and libgit2?
body: <p>Which code and how much code do the original <a href="https://github.com/git/git" rel="noreferrer">Git codebase</a> and <a href="https://libgit2.github.com/" rel="noreferrer">libgit2</a> have in common (from nothing to all Git functionality except of command line client entry points)? </p>
  
  <p>I'm primarily interested in how "stable" libgit2 is and how <strong>easily</strong> and <strong>quickly</strong> bug-fixes and/or improvements from future development in the original Git codebase can be adopted by libgit2.</p>