Add locking.
Add locking.

Special thanks to Pavlin Radoslavov <pavlin@icir.org> for testing and
fixing numerous problems.

Sponsored by:	FreeBSD Foundation
Reviewed by:	Pavlin Radoslavov <pavlin@icir.org>

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase