- Fixed bug where the truncation of long labels in SQL could produce

- Fixed bug where the truncation of long labels in SQL could produce
a label that overlapped another label that is not truncated; this
because the length threshhold for truncation was greater than
the portion of the label that remains after truncation.  These
two values have now been made the same; label_length - 6.
The effect here is that shorter column labels will be "truncated"
where they would not have been truncated before.
fixes #3396