Change computing expiration to work with memcached 1.4

Author: cnblogs-dudu

Enyim.Caching/MemcachedClient.cs

@@ -1161,6 +1161,11 @@ protected static uint GetExpiration(
                 // infinity
                 if (validFor == TimeSpan.Zero || validFor == TimeSpan.MaxValue) return 0;
 
+                if (validFor.Value.TotalSeconds <= MaxSeconds)
+                {
+                    return (uint)validFor.Value.TotalSeconds;
+                }
+
                 expiresAt = DateTime.Now.Add(validFor.Value);
             }