syslogd: Use pipe to communicate with daemon

[jfree]

Summary

Previously, syslogd's daemon process would signal that it had finished
initialization using SIGALRM. In capability mode, signal delivery is not
allowed, so use a pipe to indicate that it is ready to accept messages.

[jfree]

Remove ts and tsp variables altogether (see updated patch summary)

[jfree]

Fix conflicts after rebase. The previous revision has been squashed into a patch earlier in the stack.

[jfree]

Call die() instead of err() in waitdaemon when an error occurs so the pidfile is removed.

[markj]

usr.sbin/syslogd/syslogd.c

816–818

Since you're changing this line anyway.

867

This should be commented, since it's rather unclear what's happening here. That is, something like, "Signal our parent to let them know that we've finished initializing."

[jfree]

Address Mark's comments