Ugh - another :+1: for Linux Vs. Mac.

Linux `tail -F` waits for a non-existent file to show up (and emits status info on stderr). No such luck on OSX - #fail when no file, and no status messages.

I guess I am going to have to allow setting the `file-delay` attribute for the non-existent file situation (like with the Apache `Tailer`). And use it to relaunch the exec on a failure.