Pictures added to most error checks.

Most, if not all of the commands that check the configuration, the
state or the success of the task can now take a picture argument. By
default, the picture is an alert symbol. But it would be nice to
generate images specific to each situation.
Remove CheckOverrun().

DEX does not support, nor does it need, the check to see if the data
over ran the buffers. So this routine has been made private to the
simulator apparatii. It can no longer be called directly from within a
script.