established. This way, automatic scripts are possible that might
control the SLIP connection. It's unacceptable for a daemon that's
being controlled by a variety of signals to not leave its PID
somewhere. The file name contains the terminal path name component of
the associated tty device, so it should be unique even with multiple
parallel slattach's running. The file will be unlinked at regular exit.
Also found a minor bug in the option handling by compiling with -Wall.
c019fd7240