prevent file_scan_directory from being called on each page request

This module causes a file_scan_directory on each page load. It should cache the results of a file_scan_directory (indefinitely preferably). Doing a file scan is problematic (slow) for sites with a large number of files and exacerbated when servers are pulling files over an NFS or any remote file system.

Simply wrapping the code with a cache_get/cache_set routine resolves the issue.