Nagios remote external command daemon

This is the Nagios Remote External Commands Daemon, or NRECD for short. What it does is run a small TCP server on a Nagios monitoring server waiting for connections from remote monitored hosts. When an inbound connection is received, the nrecd daemon authenticates the remote host. If the remote host is authenticated, it is allowed to issue a Nagios external command. The external command will then be authenticated, and if it is, it will be passed to the Nagios external command pipe. There is a small program that runs on each remote host called "send_nrec" that connects to the main Nagios monitoring server and issues commands.