[ANN] posix_mq 2.0.0 - POSIX Message Queues for Ruby

POSIX message queues allow local processes to exchange data in the form
of messages. This API is distinct from that provided by System V
message queues, but provides similar functionality.

* http://bogomips.org/ruby_posix_mq/
* ruby.posix.mq@librelist.org
* git://bogomips.org/ruby_posix_mq.git
* http://bogomips.org/ruby_posix_mq/NEWS.atom.xml

Changes: a minor API change + FreeBSD fixes

Blocking methods no longer raise Errno::EINTR (to match
Ruby IO semantics, making code easier to work with).

There are also many FreeBSD-related fixes thanks to
Hleb Valoshka <375gnu@gmail.com> and small code cleanups.