wrapper for wp_enqueue_style using filemtime

enqueue_filemtime.php

<?php
// has been taken from a class, globals are just a quick and dirty workarround

// This Wrapper is one example for a simple use of cached filemtime version strings, in this case for the parent theme.
// Needs small changes to work for childtheme, javascript, plugins or register

function local_enqueue_style( $handle, $src, $deps = array(), $media = 'all' ) {
		wp_enqueue_style( $handle, get_template_directory_uri() . $src, $deps, local_get_version( get_template_directory() . $src ), $media );
	}

function local_get_version( $filepath ) {
  //see line 2
  global $file_versions;
	if ( ! is_array( $file_versions ) ) {
	  if ( ! defined( 'NO_CACHING' ) || ! NO_CACHING ) {
		  $file_versions = get_transient( 'file_versions' );
		}

		if ( ! is_array( $file_versions ) ) {
			$file_versions = array();
		}
	}

	$hash = md5( $filepath );
	if ( ! isset( $file_versions[ $hash ] ) ) {
    //see line 2
    global $update_file_versions;
		$update_file_versions = true;
		if ( file_exists( $filepath ) ) {
			$file_versions[ $hash ] = filemtime( $filepath );
		} else {
			return 'fnf'; //file not found
		}
	}

	return $file_versions[ $hash ];
}

add_action( 'shutdown', 'save_file_versions' );

function save_file_versions() {
  //see line 2
  global $update_file_versions, $file_versions;
	if ( $update_file_versions ) {
		set_transient( 'file_versions', $file_versions, 3600 );
	}
}

Very intresting! I was wondering why you used md5 for hashing the keys ?