Posix_mq 0.7.0 - 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.

Changes:

This release now works for systems other than Linux and FreeBSD
that support POSIX message queues. This is usable for systems
without mq_timedsend() or mq_timedreceive() but with the
non-timed variants (timeouts wont work).

Thanks to Tadeusz B. for testing.

Ruby posix_mq is now dual-licensed under the GPLv2 (as well as the
preferred LGPLv3) for compatibility with existing GPLv2-only code.