[Plugin: Slimbox Plugin] Fix to the regex bug breaking XHTML validation

The bug causes SlimBox to add rel attributes to all image tags that appear inside an anchor. By doing so it also breaks the standard/validation of the XHTML document by removing the trailing slash from the image and leaving it open.

The problem: regex in the slimbox_create function is incorrect since it also returns a match for those anchors that don’t link to the image file, but have an image wrapped in it, e.g.
<a href="..html"><img ... /></a>

The fix is to match the closure of the anchor:

function slimbox_create($content){
	return preg_replace('/<a(.*?)href=(.*?).(jpg|jpeg|png|gif|bmp|ico)"([.^>]*?)>/i', '<a$1href=$2.$3" rel="lightbox[roadtrip]" $4>', $content);
}

http://wordpress.org/extend/plugins/slimbox-plugin/