Fix a memory leak when cache is disabled. Debian #614347.

--- cache.c.orig	Mon Dec 16 10:33:52 2013
+++ cache.c	Mon Dec 16 10:34:02 2013
@@ -25,7 +25,7 @@ struct cache {
     time_t last_cleaned;
 };
 
-static struct cache cache;
+struct cache cache;
 
 struct node {
     struct stat stat;