Add graphics::Can() to let us determine whether the active toolkit

supports a given function.  Right now it's hardcoded to support what
we know about GD.

core/views/quick_pane.html.php

@@ -1,17 +1,22 @@
 <?php defined("SYSPATH") or die("No direct script access.") ?>
 <? if ($item->type == "photo"): ?>
+<? if (graphics::can("rotate")): ?>
 <div class="rotate-counter-clockwise"
      href="<?= url::site("quick/rotate/$item->id/ccw?csrf=" . access::csrf_token()) ?>">
   <span>
     <?= _("Rotate CCW") ?>
   </span>
 </div>
+<? endif ?>
+
 <div class="edit gDialogLink"
      href="<?= url::site("quick/form_edit/$item->id") ?>">
   <span>
     <?= _("Edit") ?>
   </span>
 </div>
+
+<? if (graphics::can("rotate")): ?>
 <div class="rotate-clockwise"
      href="<?= url::site("quick/rotate/$item->id/cw?csrf=" . access::csrf_token()) ?>">
   <span>
@@ -19,3 +24,4 @@
   </span>
 </div>
 <? endif ?>
+<? endif ?>