Make sure saved correct answer has units in NumberWithUnits()

[dpvc]

This fixes a problem with NumberWithUnits() when passed a Real MathObject created by Compute() reported in this forum post.

To test, use

loadMacros("parserNumberWithUnits.pl");
$v = Compute("sqrt(23)");
$n = NumberWithUnits($v, "m/s");

BEGIN_TEXT
$n->{correct_ans} and \($n->{correct_ans_latex_string}\)
END_TEXT

With the patch, both values should include units; without the patch, they will just be the square root with no units.