* Grab the IDs of all the image attachments in a gallery so we can get the URL
* of the next adjacent image in a gallery, or the first image (if we're
* looking at the last image in a gallery), or, in a gallery of one, just the
* Grab the IDs of all the image attachments in a gallery so we can get the URL
* of the next adjacent image in a gallery, or the first image (if we're
* looking at the last image in a gallery), or, in a gallery of one, just the