remove uploading stated from volume server.
remove the submit via volume server api.
a bit refactoring to prepare for volume format change and backward
compatibility.
Fix filer proxing http status code
Double quote etag value.
wrap etag value with double quotes
adding ttl field to volume super block
resolve directory log file error
avoid possible race condition
use error to report error
add TTL support

The volume TTL and file TTL are not necessarily the same. as long as
file TTL is smaller than volume TTL, it'll be fine.

volume TTL is used when assigning file id, e.g.
http://.../dir/assign?ttl=3h

file TTL is used when uploading
version 0.64
Adding unit tests for volume ttl.
Merge branch 'master' of https://github.com/chrislusf/weed-fs