Complete implementation of Iterator support in Horde_Image.

Complete implementation of Iterator support in Horde_Image.

This works in Imagemagick and Imagick only. GD will always return a clone of itself;
(GD doesn't support TIFF or PDF, and has no native methods for obtaining individual pages from GIF)

Multipage images (TIFF, GIF, PDF etc...) can now be either iterated as so:

<code>
// $original Image contains a multipage image
foreach($original as $page) {
  // $page is a Horde_Image object representing the single page
}
</code>

or individually select the page as so:

<code>
$page = $original->getImageAtIndex($pageNumber);
</code>

Horde_Image_Base#getImagePageCount returns the total number of pages.