Merge pull request #321 from jam7/libffi-crew_dest_dir

Changed to use #{CREW_DEST_DIR} in libffi.rb

packages/libffi.rb

 require 'package'
 
 class Libffi < Package
-  version '3.0.13'
+  version '3.0.13-1'
   source_url 'ftp://sourceware.org/pub/libffi/libffi-3.0.13.tar.gz'
   source_sha1 'f5230890dc0be42fb5c58fbf793da253155de106'
 
@@ -13,6 +13,6 @@ class Libffi < Package
   end
 
   def self.install
-    system "make", "install"
+    system "make", "DESTDIR=#{CREW_DEST_DIR}", "install"
   end
 end