title: RVM: "sha256sum nor shasum found"
body: <p>I've just installed RVM on a new machine and when switching into a directory containing a <code>.rvmrc</code> file (which I've accepted) I'm getting:</p>
  
  <pre><code>ERROR: Neither sha256sum nor shasum found in the PATH
  </code></pre>
  
  <p>I'm on OS X 10.5.8. — Probably missing something somewhere. Any ideas what's going on and how to fix this?</p>