How does require_once "check if the file has already been included"?
<p>I assume it doesn't actually hash the file contents, does it stick all of the <code>require</code>'d pathnames into an internal hash table?</p>

<p>The context for this is that I'm getting some (redeclaration) warnings that would make sense if <code>require_once</code> was getting confused by slightly different paths to the same file, and I'd obviously rather not load files multiple times.</p>
