unicorn 5.0.0.pre2 - another prerelease!

There is a minor TCP socket options are now applied to inherited
sockets, and we have native support for inheriting sockets from
systemd (by emulating the sd_listen_fds(3) function).

Dynamic changes in the application to Rack::Utils::HTTP_STATUS
codes is now supported, so you can use your own custom status
lines.

Ruby 2.2 and later is now favored for performance.
Optimizations by using constants which made sense in earlier
versions of Ruby are gone: so users of old Ruby versions
will see performance regressions.  Ruby 2.2 users should
see the same or better performance, and we have less code
as a result.

* doc: update some invalid URLs
* apply TCP socket options on inherited sockets
* reflect changes in Rack::Utils::HTTP_STATUS_CODES
* reduce constants and optimize for Ruby 2.2
* http_response: reduce size of multi-line header path
* emulate sd_listen_fds for systemd support
* test/unit/test_response.rb: compatibility with older test-unit

This also includes all changes in unicorn 5.0.0.pre1:

http://bogomips.org/unicorn-public/m/20150615225652.GA16164@dcvr.yhbt.net.html