Set output float precision & relative epsilon for DD comparison

[siddharth-krishna]

An attempted fix for #246, which was first noticed in #240. With some trial and error I set a precision of .10g (10 significant figures in exponential/scientific notation) for floating point numbers.

I also had to change the gdxdiff options to additionally use a tolerance in relative difference when comparing the output DD files to the ground truth, otherwise the higher precision output above increased the DD diff. We now use 1e-6 for both absolute Eps and relative RelEps difference tolerance. If I understand correctly how gdxdiff works, this feels like a reasonable tolerance:

AbsDiff := Abs(V1 - V2);
if  AbsDiff <= EpsAbsolute
then
  Result := true
else
  if EpsRelative > 0.0
  then
     Result := AbsDiff / (1.0 + DMin(Abs(V1), Abs(V2))) <= EpsRelative
  else
     Result := false;

Finally, we were reporting the number of lines in the output of gdxdiff, but that's only the number of sets/parameters that are different, and doesn't track improvements in number of rows different. I'm now passing the output of gdxdiff to gdxdump so that the "GDX Diff" column is more accurate and tracks number of rows in the diff.