Detect when queuedaemon/xmppdaemon parent processes die and kill the child processes.

Detect when queuedaemon/xmppdaemon parent processes die and kill the child processes.
Keeps stray daemon subprocesses from floating around when we kill the parents via a signal!

Accomplished by opening a bidirectional pipe in the parent process; the children close out the writer end and keep the reader in their open sockets list. When the parent dies, the children see that the socket's been closed out and can perform an orderly shutdown.