[Done v1.6.0] Layout Controller detects files with extensions other than .php

I was playing around with some of the sideboxes and copied /includes/modules/sideboxes/currencies.php to /includes/modules/sideboxes/classic/currencies.php (yeah, I know, but it's a local testbed). Played with it a bit and then, wanting only to temporarily disable the sidebox, renamed the classic-folder version to currencies.php~.

Imagine my surprise when Tools->Layout Boxes Controller displayed the currencies.php~ script as an available sidebox!

I haven't had a chance to inspect /admin/layout_controller.php to see what's up, but wanted to make sure that I recorded the sighting before I forgot.

I thought that was standard operaton as I'd seen it two months ago or so, but hadn't gone to ferret it out myself either.

Looking at the code though, basically any (all) files n the override directory are loaded unless named empty.txt. Was that way in 1.5.1 even.

Prior to adding the file to the directory array, there is no check to validate the extension like there is in the main directory. There also is not a check to see that the overridden file existed in the parent folder as is done with html_includes.

Addressed for v1.6.0 here: https://github.com/zencart/zencart/pull/521