unicorn 4.9.0 - TempfileReaper support in Rack 1.6

unicorn 4.9.0 - TempfileReaper support in Rack 1.6

This release supports the Rack::TempfileReaper middleware found
in rack 1.6 for cleaning up disk space used by temporary files.
We also use Rack::TempfileReaper for cleaning up large temporary
files buffered with TeeInput.  Users on rack 1.5 and earlier
will see no changes.

There's also a bunch of documentation/build system improvements.

This is likely to be the last Ruby 1.8-compatible release, unicorn 5.x
will require 1.9.3 or later as well as dropping lots of cruft (the
stupid "Status:" header in responses being the most notable).

21 changes backported from master:

      ISSUES: update with mailing list subscription
      FAQ: add entry for Rails autoflush_log
      dev: remove isolate dependency
      unicorn.gemspec: depend on test-unit 3.0
      remove RubyForge and Freecode references
      remove mongrel.rubyforge.org references
      examples: add run_once to before_fork hook example
      t/t0002-parser-error.sh: relax test for rack 1.6.0
      switch docs + website to olddoc
      README: clarify/reduce references to unicorn_rails
      gemspec: fixup olddoc migration
      GNUmakefile: fix clean gem build + reduce build cruft
      doc: update support status for Ruby versions
      fix uninstalled testing and reduce require paths
      test_socket_helper: do not depend on SO_REUSEPORT
      ISSUES: add section for bugs in other projects
      explain 11 byte magic number for self-pipe
      Links: mark Rainbows! as historical, reference yahns
      doc: document UNICORN_FD in manpage
      tee_input: support for Rack::TempfileReaper middleware
      support TempfileReaper in deployment and development envs