You might want to consider using Joomla coding standards for this like so:
$path = JPATH_SITE . '/images/slideshow/breda/';
$files = JFolder::files($path);
print_r($files);
echo '<div class="flexslider">';
echo '<ul class="slides">';
foreach($files as $file) {
echo '<li><img src="/images/slideshow/breda/';
echo $file;
echo '" alt="" title="" /></li>';
}
echo '</ul>';
echo '</div>';
print_r($file);
I haven't tested what I've quickly mocked up, so please let me know if it works or not and I can update accordingly :)
Hope this helps