detect wrong browser port

Detect when a browser incorrectly connects to the HPIB (5370) or telnet
(5371) ports and return an error message indicating the proper port to
use (5372).
v3.3

Bump to version 3.3
Better halt behavior

When halting from the front-panel menu, display "halting…", then blank
the display after Linux has actually stopped. Then it will be safe to
power down. This works for both Angstrom and Debian.