Load comments template only when comments are open or there's at least one comment

To be consistent with single.php and to ensure that an empty div (<div
id="comments" class="comments-area">) isn't outputted when both
comments are closed and there aren't any comments.
Merge pull request #132 from davidensinger/master

Load comments template only when comments are open or there's at least one comment in image.php and page.php