Update to curvefit.t tests
With the release of kdb+ 4.0 2020.07.15, the function xexp has been updated wrt. precision and performance. This necessitated a change to the curvefit.t
file to account for the precision change
With the release of kdb+ 4.0 2020.07.15, the function xexp has been updated wrt. precision and performance. This necessitated a change to the curvefit.t
file to account for the precision change