Update check-tx processor to v3.

Remove the slow encryption key calculation.
[client] Fix a bug of shutting down seafile while it's commiting.

The current code update index before commit. This will cause data
lost in the following sequence:
1. add and update index
2. restart
3. GC
4. add and update index and commit

The blocks added in the first add operation are removed by GC
since there is no commit pointing to them.
The second add operation won't add those blocks again because
the index has been updated.
[http] Avoid recursive call of bufferevent write callback when https is in use.