Support single-node DLM

Currently the DLM (distributed lock manager) is only available in a clustered environment. It would be extremely useful to have this supported on single-node systems as well.

We are trying to write generic infrastructure libraries for a variety of environments including VMs, single nodes, and clusters. We've been using the original DLM features on HP OpenVMS (formerly Digital Equipment Corp. VMS) for over twenty years in a variety of environments and have found it to be extremely useful in managing various types of access to resources, and especially with techniques for inter-process signaling. It is very frustrating to see that such a powerful interface is available, but only for a subset of platforms and thus is unusable for our applications.

Note: We've looked at the newer pthreads-based inter-process conditions, mutexes, etc., but they have restrictive recovery options which are not adequate for extremely high throughput, mission critical systems.