Branch b1_6

Use a 64-bit variable for RPC XID in case of async write error.
b=2066
i=liuy
i=nathan

lustre/include/obd.h

@@ -46,7 +46,7 @@ struct loi_oap_pages {
 struct osc_async_rc {
         int     ar_rc;
         int     ar_force_sync;
-        int     ar_min_xid;
+        __u64   ar_min_xid;
 };
 
 struct lov_oinfo {                 /* per-stripe data structure */