[ANN] unicorn 4.2.1 - Rack HTTP server for fast clients and Unix

Unicorn is an HTTP server for Rack applications designed to only serve
fast clients on low-latency, high-bandwidth connections and take
advantage of features in Unix/Unix-like kernels. Slow clients should
only be served by placing a reverse proxy capable of fully buffering
both the the request and response in between Unicorn and slow clients.

* http://unicorn.bogomips.org/
* mongrel-unicorn@rubyforge.org
* git://bogomips.org/unicorn.git
* http://unicorn.bogomips.org/NEWS.atom.xml

Changes:

* Stale pid files are detected if a pid is recycled by processes
  belonging to another user, thanks to Graham Bleach.
* nginx example config updates thanks to to Eike Herzbach.
* KNOWN_ISSUES now documents issues with apps/libs that install
  conflicting signal handlers.