Fix: Multi-volume format cannot handle on 64bit environment.

--- crc32.c.orig	Wed Apr 20 06:23:00 1994
+++ crc32.c	Fri Dec 30 23:09:44 2011
@@ -78,6 +78,7 @@ unsigned char *arg;
 int len;
 unsigned long crc;
 {
+    crc &= 0xffffffffU;
     while(--len >= 0) {
 	crc = crc >> 8 ^ crctbl[(crc & 0xff) ^ *arg++];
     }
