Add missing parentheses around vectors in IJK mode.

[dpvc]

When vectors are printed in IJK mode as part of a formula, parentheses may be needed around them, as in 2(i+3t-k), but MathObjects isn't inserting these. This PR resolves that issue.

To test, use

Context("Vector")->flags->set(ijk=>1);
TEXT(Compute("2<1,x,3>"),$BR);
TEXT(Compute("2<0,-x,0>"),$BR);
TEXT(Compute("2<0,x,0>"),$BR);

Without the patch, you will get 2*i+xj+3k, 2*-xj and 2*xj. With the patch, you will get (the correct results) 2*(i+xj+3k), 2*(-xj) and 2*xj.

See the associated bug report.

[mgage]

This works as described and resolves bug3702.