Add <unistd.h> so heritage.h is happy on macosx.

fixes #305



git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@3159 d4fa192b-c00b-0410-8231-f00ffab90ce4

bin/varnishd/cache.h

@@ -40,6 +40,7 @@
 #include <stdint.h>
 #include <string.h>
 #include <limits.h>
+#include <unistd.h>
 
 #include "vqueue.h"