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: ensure compatibility with future Rubies

* avoid deprecated rb_thread_blocking_region in Ruby 2.0/2.1
* prepare for rb_thread_blocking_region removal