Reads the data for the previous tuple for the given
relation, makes it the current tuple and will pass
it back as an associative array in tuple.
Return Values
Returns DBPLUS_ERR_NOERR
on success or a db++ error
code on failure.
Notes
Warning: This function is
EXPERIMENTAL. The behaviour of this function, the
name of this function, and anything else documented about this
function may change without notice in a future release of PHP.
Use this function at your own risk.