Turn of the reporting of datatypes in the 4th callback argument unless the

Turn of the reporting of datatypes in the 4th callback argument unless the
SHOW_DATATYPES pragma is ON.  Eliminate the NULL pointer that used to separate
the beginning of datatypes from the end of column names so that the callback
can test to see whether or not datatypes are provided.  This is an
incompatible changes, but since the prior behavior was never documented, we
will let it in. (CVS 670)

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