生成文件下载地址时，object如果是在目录中的，会导致找不到文件

[xiaofeige]

`
// buildURL builds URL
func (um urlMaker) buildURL(bucket, object string) (string, string) {
var host = ""
var path = ""

object = url.QueryEscape(object)
object = strings.Replace(object, "+", "%20", -1)

if um.Type == urlTypeCname {
	host = um.NetLoc
	path = "/" + object
} else if um.Type == urlTypeIP {
	if bucket == "" {
		host = um.NetLoc
		path = "/"
	} else {
		host = um.NetLoc
		path = fmt.Sprintf("/%s/%s", bucket, object)
	}
} else {
	if bucket == "" {
		host = um.NetLoc
		path = "/"
	} else {
		host = bucket + "." + um.NetLoc
		path = "/" + object
	}
}

return host, path

}
`

当传入的object 为 "/path/to/my-object" , 斜线都会被encode，那么就是说生成下载连接只要是这种多层目录的，都有问题