[Sass] Require fileutils in files.rb.

doc-src/SASS_CHANGELOG.md

@@ -10,6 +10,9 @@
   and is forwards-compatible with alpha-channel colors
   (to be introduced in Sass 2.4).
 
+* Added a missing require in Sass that caused crashes
+  when it was being run standalone.
+
 ## [2.2.14](http://github.com/nex3/haml/commit/2.2.14)
 
 * All Sass functions now raise explicit errors if their inputs

lib/sass/files.rb

@@ -1,5 +1,6 @@
 require 'digest/sha1'
 require 'pathname'
+require 'fileutils'
 
 module Sass
   # This module contains various bits of functionality