Extend interprocess::message_queue to be lazy initializable

[Lingxi Li <lilingxi.cs@…>]

Both shared_memory_object and mapped_region support lazy initialization, so I think message_queue should support it also. Specifically, the following methods are added to message_queue_t: 1) Default constructor 2) Move constructor/assignment operator 3) swap() 4) is_open() (naming convention follows std::basic_filebuf::is_open()) Submitted as a pull request on GitHub: ​https://github.com/boostorg/interprocess/pull/20