Add an assert to make sure 32 stays 32

git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@3848 d4fa192b-c00b-0410-8231-f00ffab90ce4

bin/varnishd/cache_hash.c

@@ -572,6 +572,7 @@ void
 HSH_Init(void)
 {
 
+	assert(DIGEST_LEN == SHA256_LEN);	/* avoid #include pollution */
 	save_hash = params->save_hash;
 	hash = heritage.hash;
 	if (hash->start != NULL)