Tor 0.2.8.6 稳定版发布性能得以提升

Tor 0.2.8.6 发布了。

改进记录如下：

New system requirements:
- Tor no longer attempts to support platforms where the “time_t” type is unsigned. (To the best of our knowledge, only OpenVMS does this, and Tor has never actually built on OpenVMS.) Closes ticket 18184.
- Tor no longer supports versions of OpenSSL with a broken implementation of counter mode. (This bug was present in OpenSSL 1.0.0, and was fixed in OpenSSL 1.0.0a.) Tor still detects, but no longer runs with, these versions.
- Tor now uses Autoconf version 2.63 or later, and Automake 1.11 or later (released in 2008 and 2009 respectively). If you are building Tor from the git repository instead of from the source distribution, and your tools are older than this, you will need to upgrade. Closes ticket 17732.

Directory authority changes:
- Update the V3 identity key for the dannenberg directory authority: it was changed on 18 November 2015. Closes task 17906. Patch by teor.
- Urras is no longer a directory authority. Closes ticket 19271.
Major features (directory system):
- Include a trial list of default fallback directories, based on an opt-in survey of suitable relays. Doing this should make clients bootstrap more quickly and reliably, and reduce the load on the directory authorities. Closes ticket 15775. Patch by teor. Candidates identified using an OnionOO script by weasel, teor, gsathya, and karsten.
- Previously only relays that explicitly opened a directory port (DirPort) accepted directory requests from clients. Now all relays, with and without a DirPort, accept and serve tunneled directory requests that they receive through their ORPort. You can disable this behavior using the new DirCache option. Closes ticket 12538.
- When bootstrapping multiple consensus downloads at a time, use the first one that starts downloading, and close the rest. This reduces failures when authorities or fallback directories are slow or down. Together with the code for feature 15775, this feature should reduces failures due to fallback churn. Implements ticket 4483. Patch by teor. Implements IPv4 portions of proposal 210 by mikeperry and teor.
Major features (security, Linux):
- When Tor starts as root on Linux and is told to switch user ID, it can now retain the capability to bind to low ports. By default, Tor will do this only when it’s switching user ID and some low ports have been configured. You can change this behavior with the new option KeepBindCapabilities. Closes ticket 8195.