c ngx_cache_purge不做考虑，据说已经停止开发了
说明：
1 我的 /root/sbin/rm_apk_list.txt 文件
[root@budong ~]# cat /root/sbin/rm_apk_list.txt /2013/08/15/38/382272/shuazanzhushou_V1.8.16_mumayi_95a91.apk
2 查看一个缓存对象，应该有些明白了吧
[root@budong ~]# more /data/mumayi/cache/0/00/db9327b60a6b3c164516117f90d9d000
KEY: /2013/10/23/43/432816/dinuochongwuDinoPets_V1.1.1_mumayi_0b399.apk HTTP/1.1 200 OK Server: nginx/1.2.6 Date: Sun, 15 Dec 2013 19:51:22 GMT Content-Type: application/vnd.android.package-archive Content-Length: 37466293 Connection: close Last-Modified: Wed, 23 Oct 2013 06:15:06 GMT Expires: Wed, 18 Dec 2013 17:35:07 GMT Cache-Control: max-age=604800 Accept-Ranges: bytes
