Stop log dumping at flight end. Print 'end' at end of log.

No reason to continue dumping data past the end of the flight now that the
logging stuff has been demonstrated to work reliably. Also, to make
automated log dumping easier, this prints out 'end' after the log data so
that aoview knows when to stop reading.

Signed-off-by: Keith Packard <keithp@keithp.com>