posix_mq 0.3.1

posix_mq 0.3.1

This fixes a misuse of the Ruby API leading to memory leaks in
cases where message queues are continually opened and closed
throughout the lifetime of the application.

Fortunately applications have little reason to repeatedly open
and close message queue descriptors: they are
multi-thread/multi-process-safe in every way imaginable and also
capable of non-blocking operation.