Ensure absolute_uri are relative to WEBROOT.

def build_absolute_uri(request, relative_url):
    """Ensure absolute_uri are relative to WEBROOT."""
    webroot = getattr(settings, 'WEBROOT', '')
    if webroot.endswith("/") and relative_url.startswith("/"):
        webroot = webroot[:-1]

    return request.build_absolute_uri(webroot + relative_url)